diff --git a/rulegen.cpp b/rulegen.cpp
index faef0515..d3c42d15 100644
--- a/rulegen.cpp
+++ b/rulegen.cpp
@@ -96,7 +96,8 @@ static const flagtype w_r3_no_road_shortcuts = Flag(36); /*< consider all errors
 /** these control the output */
 EX flagtype rdebug_flags;
 
-EX int r3_neighborhood_decision = 1; /* how far to build local for honeycombs */
+EX int r3_neighborhood_decision = 1; /* how far to build local for honeycombs, for decision trees */
+EX int r3_neighborhood_validate = 0; /* how far to build local for honeycombs, for validation */
 
 EX flagtype flags = 0;
 
@@ -1406,6 +1407,7 @@ EX pair<int, int> get_code(twalker& cw) {
     }
 
   be_solid(c);
+  if(WDIM == 3) validate_neighborhood(cw.at);
 
   twalker cd = c->dist == 0 ? twalker(c, 0) : get_parent_dir(cw);
   if(cd.at != c) ufind(cw);
@@ -2506,6 +2508,7 @@ auto hooks = addHook(hooks_configfile, 100, [] {
       param_i(max_ignore_time_pre, "max_ignore_time_pre");
       param_i(max_ignore_time_post, "max_ignore_time_post");
       param_i(r3_neighborhood_decision, "r3_neighborhood_decision");
+      param_i(r3_neighborhood_validate, "r3_neighborhood_validate");
     });
 
 EX void parse_treestate(arb::arbi_tiling& c, exp_parser& ep) {
diff --git a/rulegen3.cpp b/rulegen3.cpp
index b7cc4b7a..4926f7d2 100644
--- a/rulegen3.cpp
+++ b/rulegen3.cpp
@@ -149,11 +149,13 @@ EX int get_roadsign(twalker what) {
 using neighborhood = vector<pair<int, int>>;
 #endif
 
-map<pair<int, int>, neighborhood> all_edges;
+map<pair<int, int>, neighborhood> decision_neighborhoods;
+map<pair<int, int>, neighborhood> validate_neighborhoods;
 
 EX void build_neighborhood(twalker cw, neighborhood& ae, flagtype dec) {
   set<tcell*> seen;
   vector<pair<twalker, transmatrix> > visited;
+  vector<pair<twalker, transmatrix> > visited1;
   vector<pair<int, int>> ae1;
   auto visit = [&] (twalker tw, const transmatrix& T, int id, int dir) {
     if(seen.count(tw.at)) return;
@@ -186,16 +188,49 @@ EX void build_neighborhood(twalker cw, neighborhood& ae, flagtype dec) {
       visit(tw + j + wstep, visited[i].second * currentmap->adj(tcell_to_cell[tw.at], (tw+j).spin), i, j);
       }
     }
-  if(dec & 4) for(auto p: ae1) ae.push_back(p);
-  println(hlog, "for ", tie(cw.at->id, cw.spin), " generated all_edges structure: ", ae, " of size ", isize(ae));
+  if(dec & 4) {
+    for(auto p: ae1) ae.push_back(p);
+    for(auto v: visited1) visited1.push_back(v);
+    }
+  if(dec & 8) {
+    for(int i=0; i<isize(visited); i++) {
+      for(int j=0; j<visited[i].first.at->type; j++) {
+        twalker t = visited[i].first + j + wstep;
+        for(int s=i+1; s<isize(visited); s++) {
+          if(visited[s].first.at == t.at && ae[s].first != i)
+            ae.push_back({i, j});
+          }
+        }
+      }
+    }
   }
 
 EX neighborhood& get_decision_neighborhood(twalker cw) {
-  auto& ae = all_edges[{cw.at->id, cw.spin}];
-  if(ae.empty()) build_neighborhood(cw, ae, r3_neighborhood_decision);
+  auto& ae = decision_neighborhoods[{cw.at->id, cw.spin}];
+  if(ae.empty()) {
+    build_neighborhood(cw, ae, r3_neighborhood_decision);
+    println(hlog, "built decision neighborhood for ", tie(cw.at->id, cw.spin), " of size ", isize(ae));
+    }
   return ae;
   }
 
+EX neighborhood& get_validate_neighborhood(twalker cw) {
+  auto& ae = validate_neighborhoods[{cw.at->id, cw.spin}];
+  if(ae.empty()) {
+    build_neighborhood(cw, ae, r3_neighborhood_validate);
+    println(hlog, "built validate neighborhood for ", tie(cw.at->id, cw.spin), " of size ", isize(ae));
+    }
+  return ae;
+  }
+
+EX void validate_neighborhood(twalker cw) {
+  if(!r3_neighborhood_validate) return;
+  auto& ae = get_validate_neighborhood(cw);
+  vector<twalker> list = { cw };
+  for(auto v: ae) if(v.first != -1)
+    list.push_back(list[v.first] + v.second + wstep);
+  }
+
 int last_qroad;
 
 vector<vector<pair<int,int>>> possible_parents;