diff --git a/FixedOrderGen/include/PhaseSpacePoint.hh b/FixedOrderGen/include/PhaseSpacePoint.hh
index 9e49a40..e244662 100644
--- a/FixedOrderGen/include/PhaseSpacePoint.hh
+++ b/FixedOrderGen/include/PhaseSpacePoint.hh
@@ -1,202 +1,210 @@
 /** \file PhaseSpacePoint.hh
  *  \brief Contains the PhaseSpacePoint Class
  */
 
 #pragma once
 
 #include <bitset>
 #include <vector>
 
 #include "RHEJ/utility.hh"
 #include "RHEJ/Event.hh"
 #include "RHEJ/PDG_codes.hh"
 #include "RHEJ/PDF.hh"
 #include "RHEJ/RNG.hh"
 
 #include "Status.hh"
 #include "JetParameters.hh"
 #include "HiggsProperties.hh"
 
 namespace HEJFOG{
   class Process;
 
   using RHEJ::Particle;
   //! A point in resummation phase space
   class PhaseSpacePoint{
   public:
     //! Default PhaseSpacePoint Constructor
     PhaseSpacePoint() = default;
 
     //! PhaseSpacePoint Constructor
     /**
      * @param proc             The process to generate
      * @param jet_def          The Jet Definition Used
      * @param jetptmin         Minimum Jet Transverse Momentum
      * @param rapmax           Maximum parton rapidity
      * @param pdf              The pdf set (used for sampling)
      * @param subl_chance      Chance to turn a potentially subleading
      *                         emission (uno or central qqx) into an actual one
      *
      * Initially, only FKL phase space points are generated. subl_chance gives
      * the change of turning one emissions into a subleading configuration,
      * i.e. either unordered or central quark/anti-quark pair. Unordered
      * emissions require that the most extremal emission in any direction is
      * a quark or anti-quark and the next emission is a gluon. Quark/anti-quark
      * pairs are only generated for W processes. At most one subleading
      * emission will be generated in this way.
      */
     PhaseSpacePoint(
       Process const & proc,
       JetParameters const & jet_properties,
       RHEJ::PDF & pdf, double E_beam,
       double subl_chance,
       HiggsProperties const & higgs_properties,
       RHEJ::RNG & ran
     );
 
     //! Get Weight Function
     /**
      * @returns        Weight of Event
      */
     double weight() const{
       return weight_;
     }
 
     Status status() const{
       return status_;
     }
 
     //! Get Incoming Function
     /**
      * @returns        Incoming Particles
      */
     std::array<Particle, 2> const & incoming() const{
       return incoming_;
     }
 
     //! Get Outgoing Function
     /**
      * @returns        Outgoing Particles
      */
     std::vector<Particle> const & outgoing() const{
       return outgoing_;
     }
 
     std::unordered_map<int, std::vector<Particle>> const & decays() const{
       return decays_;
     }
 
   private:
     /**
      * \internal
      * \brief Generate LO parton momentum
      *
      * @param count             Number of partons to generate
      * @param is_pure_jets      If true ensures momentum conservation in x and y
      * @param jet_param         Jet properties to fulfil
      * @param max_pt            max allowed pt for a parton (typically E_CMS)
      * @param ran               Random Number Generator
      *
      * @returns                 Momentum of partons
      *
      * Ensures that each parton is in its own jet.
      * Generation is independent of parton flavour. Output is sorted in rapidity.
      */
     std::vector<fastjet::PseudoJet> gen_LO_partons(
         int count, bool is_pure_jets,
         JetParameters const & jet_param,
         double max_pt,
         RHEJ::RNG & ran
     );
     Particle gen_boson(
         RHEJ::ParticleID bosonid, double mass, double width,
         RHEJ::RNG & ran
     );
     template<class ParticleMomenta>
     fastjet::PseudoJet gen_last_momentum(
         ParticleMomenta const & other_momenta,
         double mass_square, double y
     ) const;
 
     bool jets_ok(
         std::vector<fastjet::PseudoJet> const & Born_jets,
         std::vector<fastjet::PseudoJet> const & partons
     ) const;
     /**
      * \internal
      * \brief Generate incoming partons according to the PDF
      *
      * @param uf                Scale used in the PDF
      */
     void reconstruct_incoming(
         Process const & proc,
         RHEJ::PDF & pdf, double E_beam,
         double uf,
         RHEJ::RNG & ran
     );
+    /**
+     * @internal
+     * @brief Returns list of all allowed initial states partons
+     */
+    std::array<std::bitset<11>,2> filter_partons(
+        Process const & proc,RHEJ::RNG & ran
+    );
     RHEJ::ParticleID generate_incoming_id(
         size_t beam_idx, double x, double uf, RHEJ::PDF & pdf,
         std::bitset<11> allowed_partons, RHEJ::RNG & ran
     );
 
     bool momentum_conserved(double ep) const;
 
     RHEJ::Particle const & most_backward_FKL(
         std::vector<RHEJ::Particle> const & partons
     ) const;
     RHEJ::Particle const & most_forward_FKL(
         std::vector<RHEJ::Particle> const & partons
     ) const;
     RHEJ::Particle & most_backward_FKL(std::vector<RHEJ::Particle> & partons) const;
     RHEJ::Particle & most_forward_FKL(std::vector<RHEJ::Particle> & partons) const;
     bool extremal_FKL_ok(
         std::vector<fastjet::PseudoJet> const & partons
     ) const;
     double random_normal(double stddev, RHEJ::RNG & ran);
     /**
+     * @internal
      * @brief Turns a FKL configuration into a subleading one
      *
      * @param chance            Change to switch to subleading configuration
      * @param proc              Process to decide which subleading
      *                          configurations are allowed
      *
      * With a chance of "chance" the FKL configuration is either turned into
      * a unordered configuration or, for A/W/Z bosons, a configuration with
      * a central quark/anti-quark pair.
      */
     void maybe_turn_to_subl(double chance, Process const & proc, RHEJ::RNG & ran);
     void turn_to_uno(bool can_be_uno_backward, bool can_be_uno_forward, RHEJ::RNG & ran);
     void turn_to_qqx(RHEJ::RNG & ran);
     std::vector<Particle> decay_boson(
         RHEJ::Particle const & parent,
         std::vector<Decay> const & decays,
         RHEJ::RNG & ran
     );
     /// @brief setup outgoing partons to ensure correct coupling to boson
     void couple_boson(RHEJ::ParticleID boson, RHEJ::RNG & ran);
     Decay select_decay_channel(
         std::vector<Decay> const & decays,
         RHEJ::RNG & ran
     );
     double gen_hard_pt(
         int np, double ptmin, double ptmax, double y,
         RHEJ::RNG & ran
     );
     double gen_soft_pt(int np, double ptmax, RHEJ::RNG & ran);
     double gen_parton_pt(
         int count, JetParameters const & jet_param, double ptmax, double y,
         RHEJ::RNG & ran
     );
 
 
     double weight_;
 
     Status status_;
 
     std::array<Particle, 2> incoming_;
     std::vector<Particle> outgoing_;
     //! Particle decays in the format {outgoing index, decay products}
     std::unordered_map<int, std::vector<Particle>> decays_;
   };
   RHEJ::UnclusteredEvent to_UnclusteredEvent(PhaseSpacePoint const & psp);
 }
diff --git a/FixedOrderGen/src/PhaseSpacePoint.cc b/FixedOrderGen/src/PhaseSpacePoint.cc
index a5adbfc..8fba6b8 100644
--- a/FixedOrderGen/src/PhaseSpacePoint.cc
+++ b/FixedOrderGen/src/PhaseSpacePoint.cc
@@ -1,650 +1,676 @@
 #include "PhaseSpacePoint.hh"
 
 #include <random>
 #include <algorithm>
 
 #include "RHEJ/Constants.hh"
 #include "RHEJ/kinematics.hh"
 #include "RHEJ/utility.hh"
 #include "RHEJ/exceptions.hh"
 
 #include "Process.hh"
 
 #include <CLHEP/Random/Randomize.h>
 #include <CLHEP/Random/RanluxEngine.h>
 
 using namespace RHEJ;
 
 namespace HEJFOG{
 
   static_assert(
       std::numeric_limits<double>::has_quiet_NaN,
       "no quiet NaN for double"
   );
   constexpr double NaN = std::numeric_limits<double>::quiet_NaN();
   RHEJ::UnclusteredEvent to_UnclusteredEvent(PhaseSpacePoint const & psp){
     RHEJ::UnclusteredEvent result;
     result.incoming = psp.incoming();
     std::sort(
         begin(result.incoming), end(result.incoming),
         [](Particle o1, Particle o2){return o1.p.pz()<o2.p.pz();}
     );
     assert(result.incoming.size() == 2);
     result.outgoing = psp.outgoing();
     assert(
         std::is_sorted(
             begin(result.outgoing), end(result.outgoing),
             RHEJ::rapidity_less{}
         )
     );
     assert(result.outgoing.size() >= 2);
     result.decays = psp.decays();
     result.central.mur = NaN;
     result.central.muf = NaN;
     result.central.weight = psp.weight();
     return result;
   }
 
   namespace{
     bool can_swap_to_uno(
         RHEJ::Particle const & p1, RHEJ::Particle const & p2
     ){
       return is_parton(p1)
         && p1.type != pid::gluon
         && p2.type == pid::gluon;
     }
 
     size_t count_gluons(std::vector<Particle>::const_iterator first,
       std::vector<Particle>::const_iterator last){
       return std::count_if(first, last, [](Particle const & p)
         {return p.type == pid::gluon;});
     }
 
     /** assumes FKL configurations between first and last,
      * else there can be a quark in a non-extreme position
      * e.g. uno configuration gqg would pass
      */
     bool can_change_to_qqx(
       std::vector<Particle>::const_iterator first,
       std::vector<Particle>::const_iterator last){
       return 1 < count_gluons(first,last);
     }
 
     bool is_AWZ_proccess(Process const & proc){
       return proc.boson && is_AWZ_boson(*proc.boson);
     }
   }
 
   void PhaseSpacePoint::maybe_turn_to_subl(
       double chance,
       Process const & proc,
       RHEJ::RNG & ran
   ){
     if(proc.njets <= 2) return;
     assert(outgoing_.size() >= 2);
 
     // decide what kind of subleading process is allowed
     bool allow_uno = false;
     const size_t nout = outgoing_.size();
     const bool can_be_uno_backward = can_swap_to_uno(
       outgoing_[0], outgoing_[1]
     );
     const bool can_be_uno_forward = can_swap_to_uno(
       outgoing_[nout-1], outgoing_[nout-2]
     );
     allow_uno = can_be_uno_backward || can_be_uno_forward;
 
     bool allow_qqx = false;
     if(is_AWZ_proccess(proc)) {
       allow_qqx = can_change_to_qqx(outgoing_.cbegin(), outgoing_.cend());
       if(incoming_[0].type == pid::gluon && incoming_[1].type == pid::gluon) {
         /// enforce qqx for initial gg
         allow_uno = false;
         chance = 1.;
       }
     }
 
     if(!allow_uno && !allow_qqx) return;
     if(ran.flat() < chance){
       weight_ /= chance;
       if(allow_uno && !allow_qqx){
           turn_to_uno(can_be_uno_backward, can_be_uno_forward, ran);
       } else if (!allow_uno && allow_qqx) {
         turn_to_qqx(ran);
       } else {
         assert( allow_uno && allow_qqx);
         if(ran.flat() < 0.5) turn_to_uno(can_be_uno_backward, can_be_uno_forward, ran);
         else turn_to_qqx(ran);
         weight_ *= 2.;
       }
     } else weight_ /= 1 - chance;
 
   }
 
   void PhaseSpacePoint::turn_to_uno(
       const bool can_be_uno_backward, const bool can_be_uno_forward,
       RHEJ::RNG & ran
   ){
     if(!can_be_uno_backward && !can_be_uno_forward) return;
     const size_t nout = outgoing_.size();
     if(can_be_uno_backward && can_be_uno_forward){
       if(ran.flat() < 0.5){
         std::swap(outgoing_[0].type, outgoing_[1].type);
       } else {
         std::swap(outgoing_[nout-1].type, outgoing_[nout-2].type);
       }
       weight_ *= 2.;
     } else if(can_be_uno_backward){
       std::swap(outgoing_[0].type, outgoing_[1].type);
     } else {
       assert(can_be_uno_forward);
       std::swap(outgoing_[nout-1].type, outgoing_[nout-2].type);
     }
   }
 
   void PhaseSpacePoint::turn_to_qqx(RHEJ::RNG & ran){
     /// find first and last gluon in FKL chain
     auto first = std::find_if(outgoing_.begin(), outgoing_.end(),
       [](Particle const & p){return p.type == pid::gluon;});
     std::vector<Particle*> FKL_gluons;
     for(auto p = first; p<outgoing_.end(); ++p){
       if((*p).type == pid::gluon) FKL_gluons.push_back(&*p);
       else if(is_quark(*p) || is_antiquark(*p)) break;
     }
     const size_t ng = FKL_gluons.size();
     if(ng < 2)
       throw std::logic_error("not enough gluons to create qqx");
     // select flavour of quark
     const double r1 = 2.*ran.flat()-1.;
     weight_ *= n_f*2;
     int flavour = pid::down;
     for (double sum = 1./n_f; sum < std::abs(r1); sum += 1./n_f)
       ++flavour;
     flavour*=r1<0.?-1:1;
     // select gluon for switch
     const size_t idx = floor((ng-1) * ran.flat());
     weight_ *= (ng-1);
     FKL_gluons[idx]->type = ParticleID(flavour);
     FKL_gluons[idx+1]->type = ParticleID(-flavour);
   }
 
   template<class ParticleMomenta>
   fastjet::PseudoJet PhaseSpacePoint::gen_last_momentum(
       ParticleMomenta const & other_momenta,
       const double mass_square, const double y
   ) const {
     std::array<double,2> pt{0.,0.};
     for (auto const & p: other_momenta) {
       pt[0]-= p.px();
       pt[1]-= p.py();
     }
 
     const double mperp = sqrt(pt[0]*pt[0]+pt[1]*pt[1]+mass_square);
     const double pz=mperp*sinh(y);
     const double E=mperp*cosh(y);
 
     return {pt[0], pt[1], pz, E};
   }
 
   PhaseSpacePoint::PhaseSpacePoint(
     Process const & proc,
     JetParameters const & jet_param,
     RHEJ::PDF & pdf, double E_beam,
     double subl_chance,
     HiggsProperties const & h,
     RHEJ::RNG & ran
   )
   {
     assert(proc.njets >= 2);
     status_ = good;
     weight_ = 1;
 
     const int nout = proc.njets + (proc.boson?1:0);
     outgoing_.reserve(nout);
 
     // generate parton momenta
     const bool is_pure_jets = !proc.boson;
     auto partons = gen_LO_partons(
         proc.njets, is_pure_jets, jet_param, E_beam, ran
     );
     // pre fill flavour with gluons
     for(auto&& p_out: partons) {
       outgoing_.emplace_back(Particle{pid::gluon, std::move(p_out)});
     }
     if(status_ != good) return;
 
     if(proc.boson){
       switch (*proc.boson) {
       case pid::Higgs:{
         auto Hparticle=gen_boson(pid::higgs, h.mass, h.width, ran);
         auto pos=std::upper_bound(
             begin(outgoing_),end(outgoing_),Hparticle,rapidity_less{}
         );
         outgoing_.insert(pos, Hparticle);
         if(! h.decays.empty()){
           const int boson_idx = std::distance(begin(outgoing_), pos);
           decays_.emplace(
               boson_idx,
               decay_boson(outgoing_[boson_idx], h.decays, ran)
           );
         }
         break;
       }
       case pid::Wp:{
         /// @TODO change label names, currently this is just a relabel Higgs
         auto Hparticle=gen_boson(pid::Wp, h.mass, h.width, ran);
         auto pos=std::upper_bound(
             begin(outgoing_),end(outgoing_),Hparticle,rapidity_less{}
         );
         outgoing_.insert(pos, Hparticle);
         if(! h.decays.empty()){
           const int boson_idx = std::distance(begin(outgoing_), pos);
           decays_.emplace(
               boson_idx,
               decay_boson(outgoing_[boson_idx], h.decays, ran)
           );
         }
         break;
       }
       case pid::Wm:{
         /// @TODO change label names, currently this is just a relabel Higgs
         auto Hparticle=gen_boson(pid::Wm, h.mass, h.width, ran);
         auto pos=std::upper_bound(
             begin(outgoing_),end(outgoing_),Hparticle,rapidity_less{}
         );
         outgoing_.insert(pos, Hparticle);
         if(! h.decays.empty()){
           const int boson_idx = std::distance(begin(outgoing_), pos);
           decays_.emplace(
               boson_idx,
               decay_boson(outgoing_[boson_idx], h.decays, ran)
           );
         }
         break;
       }
       case pid::photon:
       case pid::Z:
       default:
         throw std::logic_error("Emission of boson of unsupported type");
       }
     }
     // normalisation of momentum-conserving delta function
     weight_ *= pow(2*M_PI, 4);
 
     reconstruct_incoming(proc, pdf, E_beam, jet_param.min_pt, ran);
     if(status_ != good) return;
     // set outgoing states
     most_backward_FKL(outgoing_).type = incoming_[0].type;
     most_forward_FKL(outgoing_).type = incoming_[1].type;
 
     maybe_turn_to_subl(subl_chance, proc, ran);
 
     if(proc.boson) couple_boson(*proc.boson, ran);
   }
 
   double PhaseSpacePoint::gen_hard_pt(
       int np , double ptmin, double ptmax, double y,
       RHEJ::RNG & ran
   ) {
     // heuristic parameters for pt sampling
     const double ptpar = ptmin + np/5.;
     const double arg_small_y = atan((ptmax - ptmin)/ptpar);
     const double y_cut = 3.;
 
     const double r1 = ran.flat();
     if(y < y_cut){
       const double pt = ptmin + ptpar*tan(r1*arg_small_y);
       const double temp = cos(r1*arg_small_y);
       weight_ *= pt*ptpar*arg_small_y/(temp*temp);
       return pt;
     }
 
     const double ptpar2 = ptpar/(1 + 5*(y-y_cut));
     const double temp = 1. - std::exp((ptmin-ptmax)/ptpar2);
     const double pt = ptmin - ptpar2*std::log(1-r1*temp);
     weight_ *= pt*ptpar2*temp/(1-r1*temp);
     return pt;
   }
 
   double PhaseSpacePoint::gen_soft_pt(int np, double max_pt, RHEJ::RNG & ran) {
     constexpr double ptpar = 4.;
 
     const double r = ran.flat();
     const double pt = max_pt + ptpar/np*std::log(r);
     weight_ *= pt*ptpar/(np*r);
     return pt;
   }
 
   double PhaseSpacePoint::gen_parton_pt(
       int count, JetParameters const & jet_param, double max_pt, double y,
       RHEJ::RNG & ran
   ) {
     constexpr double p_small_pt = 0.02;
 
     if(! jet_param.peak_pt) {
        return gen_hard_pt(count, jet_param.min_pt, max_pt, y, ran);
     }
     const double r = ran.flat();
     if(r > p_small_pt) {
       weight_ /= 1. - p_small_pt;
       return gen_hard_pt(count, *jet_param.peak_pt, max_pt, y, ran);
     }
     weight_ /= p_small_pt;
     const double pt =  gen_soft_pt(count, *jet_param.peak_pt, ran);
     if(pt < jet_param.min_pt) {
       weight_=0.0;
       status_ = not_enough_jets;
       return jet_param.min_pt;
     }
     return pt;
   }
 
   std::vector<fastjet::PseudoJet> PhaseSpacePoint::gen_LO_partons(
       int np, bool is_pure_jets,
       JetParameters const & jet_param,
       double max_pt,
       RHEJ::RNG & ran
   ){
     if (np<2) throw std::invalid_argument{"Not enough partons in gen_LO_partons"};
 
     weight_ /= pow(16.*pow(M_PI,3),np);
     weight_ /= std::tgamma(np+1); //remove rapidity ordering
     std::vector<fastjet::PseudoJet> partons;
     partons.reserve(np);
     for(int i = 0; i < np; ++i){
       const double y = -jet_param.max_y + 2*jet_param.max_y*ran.flat();
       weight_ *= 2*jet_param.max_y;
 
       const bool is_last_parton = i+1 == np;
       if(is_pure_jets && is_last_parton) {
         constexpr double parton_mass_sq = 0.;
         partons.emplace_back(gen_last_momentum(partons, parton_mass_sq, y));
         break;
       }
 
       const double phi = 2*M_PI*ran.flat();
       weight_ *= 2.0*M_PI;
 
       const double pt = gen_parton_pt(np, jet_param, max_pt, y, ran);
       if(weight_ == 0.0) return {};
 
       partons.emplace_back(fastjet::PtYPhiM(pt, y, phi));
       assert(jet_param.min_pt <= partons[i].pt());
       assert(partons[i].pt() <= max_pt+1e-5);
     }
     // Need to check that at LO, the number of jets = number of partons;
     fastjet::ClusterSequence cs(partons, jet_param.def);
     auto cluster_jets=cs.inclusive_jets(jet_param.min_pt);
     if (cluster_jets.size()!=unsigned(np)){
       weight_=0.0;
       status_ = not_enough_jets;
       return {};
     }
 
     std::sort(begin(partons), end(partons), rapidity_less{});
 
     return partons;
   }
 
   Particle PhaseSpacePoint::gen_boson(
       RHEJ::ParticleID bosonid, double mass, double width,
       RHEJ::RNG & ran
   ){
     // Usual phase space measure
     weight_ /= 16.*pow(M_PI, 3);
 
     // Generate a y Gaussian distributed around 0
     /// @TODO: magic number only for Higgs
     /// @TODO better sampling for W
     const double y = random_normal(1.6, ran);
     const double r1 = ran.flat();
     const double sH = mass*(
         mass + width*tan(M_PI/2.*r1 + (r1-1.)*atan(mass/width))
     );
 
     auto p = gen_last_momentum(outgoing_, sH, y);
 
     return Particle{bosonid, std::move(p)};
   }
 
   Particle const & PhaseSpacePoint::most_backward_FKL(
       std::vector<Particle> const & partons
   ) const{
     if(!RHEJ::is_parton(partons[0])) return partons[1];
     return partons[0];
   }
 
   Particle const & PhaseSpacePoint::most_forward_FKL(
       std::vector<Particle> const & partons
   ) const{
     const size_t last_idx = partons.size() - 1;
     if(!RHEJ::is_parton(partons[last_idx])) return partons[last_idx-1];
     return partons[last_idx];
   }
 
   Particle & PhaseSpacePoint::most_backward_FKL(
       std::vector<Particle> & partons
   ) const{
     if(!RHEJ::is_parton(partons[0])) return partons[1];
     return partons[0];
   }
 
   Particle & PhaseSpacePoint::most_forward_FKL(
       std::vector<Particle> & partons
   ) const{
     const size_t last_idx = partons.size() - 1;
     if(!RHEJ::is_parton(partons[last_idx])) return partons[last_idx-1];
     return partons[last_idx];
   }
 
   namespace {
     /// partons are ordered: even = anti, 0 = gluon
     ParticleID index_to_pid(size_t i){
       if(!i) return pid::gluon;
       return static_cast<ParticleID>(i%2?(i+1)/2:-i/2);
     }
 
+    /// partons are ordered: even = anti, 0 = gluon
+    size_t pid_to_index(ParticleID id){
+      if(id==pid::gluon) return 0;
+      return id>0?id*2-1:abs(id)*2;
+    }
+
+    std::bitset<11> init_allowed(ParticleID const id){
+      if(abs(id) == pid::proton)
+        return ~0;
+      std::bitset<11> out = 0;
+      if(is_parton(id))
+        out[pid_to_index(id)] = 1;
+      return out;
+    }
+
     /// decides which "index" (see index_to_pid) are allowed for process
-    std::bitset<11> switch_allowed(Process const & proc){
+    std::bitset<11> allowed_quarks(ParticleID const boson){
       std::bitset<11> allowed = ~0;
-      allowed[0] = 0; // no gluon
-      if(abs(*proc.boson) == pid::Wp){
-        // special case W+2j:
-        // Wp: anti-down or up-type quark, no b/t -> 0001100110(0) = 204
-        // Wm: down or anti-up-type quark, no b/t -> 0010011001(0) = 306
-        allowed &= (*proc.boson)>0?204:306;
+      if(abs(boson) == pid::Wp){
+        // special case W:
+        // Wp: anti-down or up-type quark, no b/t -> 0001100110(1) = 205
+        // Wm: down or anti-up-type quark, no b/t -> 0010011001(1) = 307
+        allowed = boson>0?205:307;
       }
       return allowed;
     }
   }
 
+  std::array<std::bitset<11>,2> PhaseSpacePoint::filter_partons(
+      Process const & proc, RHEJ::RNG & ran
+  ){
+    std::array<std::bitset<11>,2> allowed_partons{
+        init_allowed(proc.incoming[0]),
+        init_allowed(proc.incoming[1])
+      };
+    // special case A/W/Z + 2/3 jets
+    if(is_AWZ_proccess(proc) && (proc.njets < 4)){
+      auto allowed(allowed_quarks(*proc.boson));
+      if(proc.njets == 2) allowed[0]=0;   // no initial gluon for 2j
+      std::array<std::bitset<11>,2> const maybe_partons{
+        allowed_partons[0]&allowed, allowed_partons[1]&allowed};
+
+      if(maybe_partons[0].any() && maybe_partons[1].any()){
+        // two options to get allowed initial state => choose one at random
+        const size_t idx = ran.flat() < 0.5;
+        allowed_partons[idx] = maybe_partons[idx];
+      } else if(maybe_partons[0].any()) {
+        // only first possible => choose
+        allowed_partons[0] = maybe_partons[0];
+      } else if(maybe_partons[1].any()) {
+        // only second possible => choose
+        allowed_partons[1] = maybe_partons[1];
+      } else{
+        throw std::invalid_argument{"Incoming state not allowed."};
+      }
+    }
+    return allowed_partons;
+  }
+
   void PhaseSpacePoint::reconstruct_incoming(
       Process const & proc,
       RHEJ::PDF & pdf, double E_beam,
       double uf,
       RHEJ::RNG & ran
   ){
     std::tie(incoming_[0].p, incoming_[1].p) = incoming_momenta(outgoing_);
     // calculate xa, xb
     const double sqrts=2*E_beam;
     const double xa=(incoming_[0].p.e()-incoming_[0].p.pz())/sqrts;
     const double xb=(incoming_[1].p.e()+incoming_[1].p.pz())/sqrts;
     // abort if phase space point is outside of collider energy reach
     if (xa>1. || xb>1.){
       weight_=0;
       status_ = too_much_energy;
       return;
     }
     // pick pdfs
     /** @TODO
      *  ufa, ufb don't correspond to our final scale choice.
      *  The reversed HEJ scale generators currently expect a full event as input,
      *  so fixing this is not completely trivial
      */
     auto const & ids = proc.incoming;
-    std::array<std::bitset<11>,2> allowed_partons{~0,~0};
-    // special case A/W/Z+2j: needs one quark initially
-    if(proc.njets == 2 && is_AWZ_proccess(proc)){
-    // @TODO optimise: do not allow dd initial for Wp, also for 3j
-      if(ids[0] != pid::gluon && ids[1] != pid::gluon){
-        // both can be quarks => force one to be a gluon
-        weight_*=2.;
-        allowed_partons[ran.flat() < 0.5] = switch_allowed(proc);
-      } else if(ids[0] == pid::gluon) {
-        if(ids[1] == pid::gluon) {
-          throw RHEJ::not_implemented{
-            "W+2 jet process requires at least one initial quark"
-          };
-        }
-        // first gluon -> second has to be quark
-        allowed_partons[1] = switch_allowed(proc);
-      } else {
-        // second gluon -> first has to be quark
-        allowed_partons[0] = switch_allowed(proc);
-      }
-    }
+    std::array<std::bitset<11>,2> allowed_partons(filter_partons(proc, ran));
     for(size_t i = 0; i < 2; ++i){
       if(ids[i] == pid::proton || ids[i] == pid::p_bar){
         incoming_[i].type =
           generate_incoming_id(i, i?xb:xa, uf, pdf, allowed_partons[i], ran);
       } else {
+        assert(allowed_partons[i][pid_to_index(ids[i])]);
         incoming_[i].type = ids[i];
       }
     }
     assert(momentum_conserved(1e-7));
   }
 
   RHEJ::ParticleID PhaseSpacePoint::generate_incoming_id(
       size_t const beam_idx, double const x, double const uf,
       RHEJ::PDF & pdf, std::bitset<11> allowed_partons, RHEJ::RNG & ran
   ){
     std::array<double,11> pdf_wt;
     pdf_wt[0] = allowed_partons[0]?fabs(pdf.pdfpt(beam_idx,x,uf,pid::gluon)):0.;
     double pdftot = pdf_wt[0];
     for(size_t i = 1; i < pdf_wt.size(); ++i){
       pdf_wt[i] = allowed_partons[i]?4./9.*fabs(pdf.pdfpt(beam_idx,x,uf,index_to_pid(i))):0;
       pdftot += pdf_wt[i];
     }
     const double r1 = pdftot * ran.flat();
     double sum = 0;
     for(size_t i=0; i < pdf_wt.size(); ++i){
       if (r1 < (sum+=pdf_wt[i])){
         weight_*= pdftot/pdf_wt[i];
         return index_to_pid(i);
       }
     }
     std::cerr << "Error in choosing incoming parton: "<<x<<" "<<uf<<" "
       <<sum<<" "<<pdftot<<" "<<r1<<std::endl;
     throw std::logic_error{"Failed to choose parton flavour"};
   }
 
   namespace {
     bool is_up_type(Particle const & part){
       return RHEJ::is_anyquark(part) && !(abs(part.type)%2);
     }
     bool is_down_type(Particle const & part){
       return RHEJ::is_anyquark(part) && abs(part.type)%2;
     }
   }
 
   void PhaseSpacePoint::couple_boson(
     RHEJ::ParticleID const boson, RHEJ::RNG & ran
   ){
     if(abs(boson) != pid::Wp) return; // only matters for W
 
     // find all possible quarks
     const int sign_W = boson>0?1:-1;
     std::vector<Particle*> allowed_parts;
     for(auto & part: outgoing_){
       // Wp -> up OR anti-down, Wm -> anti-up OR down, no bottom
       if ( abs(part.type)<5
         && ( (sign_W*part.type > 0 && is_up_type(part))
           || (sign_W*part.type < 0 && is_down_type(part)) ) )
         allowed_parts.push_back(&part);
     }
     if(!allowed_parts.size()){
       /// @TODO do not allow such states in the generation
       status_=wrong_final_state;
       return;
     }
 
     // select one and flip it
     size_t idx = 0;
     if(allowed_parts.size() > 1){
       /// @TODO more efficient sampling
       ///       old code: probability[i] = exp(parton[i].y - W.y)
       idx = floor(ran.flat()*allowed_parts.size());
       weight_ *= allowed_parts.size();
     }
     allowed_parts[idx]->type =
       static_cast<ParticleID>( allowed_parts[idx]->type - sign_W );
   }
 
   double PhaseSpacePoint::random_normal(
       double stddev,
       RHEJ::RNG & ran
   ){
     const double r1 = ran.flat();
     const double r2 = ran.flat();
     const double lninvr1 = -log(r1);
     const double result = stddev*sqrt(2.*lninvr1)*cos(2.*M_PI*r2);
     weight_ *= exp(result*result/(2*stddev*stddev))*sqrt(2.*M_PI)*stddev;
     return result;
   }
 
   bool PhaseSpacePoint::momentum_conserved(double ep) const{
     fastjet::PseudoJet diff;
     for(auto const & in: incoming()) diff += in.p;
     for(auto const & out: outgoing()) diff -= out.p;
     return nearby_ep(diff, fastjet::PseudoJet{}, ep);
   }
 
   Decay PhaseSpacePoint::select_decay_channel(
       std::vector<Decay> const & decays,
       RHEJ::RNG & ran
   ){
     double br_total = 0.;
     for(auto const & decay: decays) br_total += decay.branching_ratio;
     // adjust weight
     // this is given by (channel branching ratio)/(chance to pick channel)
     // where (chance to pick channel) =
     //       (channel branching ratio)/(total branching ratio)
     weight_ *= br_total;
     const double r1 = br_total*ran.flat();
     double br_sum = 0.;
     for(auto const & decay: decays){
       br_sum += decay.branching_ratio;
       if(r1 < br_sum) return decay;
     }
     throw std::logic_error{"unreachable"};
   }
 
   std::vector<Particle> PhaseSpacePoint::decay_boson(
       RHEJ::Particle const & parent,
       std::vector<Decay> const & decays,
       RHEJ::RNG & ran
   ){
     const auto channel = select_decay_channel(decays, ran);
     if(channel.products.size() != 2){
       throw RHEJ::not_implemented{
         "only decays into two particles are implemented"
       };
     }
     std::vector<Particle> decay_products(channel.products.size());
     for(size_t i = 0; i < channel.products.size(); ++i){
       decay_products[i].type = channel.products[i];
     }
     // choose polar and azimuth angle in parent rest frame
     const double E = parent.m()/2;
     const double theta = 2.*M_PI*ran.flat();
     const double cos_phi = 2.*ran.flat()-1.;
     const double sin_phi = sqrt(1. - cos_phi*cos_phi);  // Know 0 < phi < pi
     const double px = E*cos(theta)*sin_phi;
     const double py = E*sin(theta)*sin_phi;
     const double pz = E*cos_phi;
     decay_products[0].p.reset(px, py, pz, E);
     decay_products[1].p.reset(-px, -py, -pz, E);
     for(auto & particle: decay_products) particle.p.boost(parent.p);
     return decay_products;
   }
 }