diff --git a/arbitrile.cpp b/arbitrile.cpp
index e411c9b4..c7bf606b 100644
--- a/arbitrile.cpp
+++ b/arbitrile.cpp
@@ -71,6 +71,7 @@ struct arbi_tiling {
 
   int order;
   bool have_line, have_ph, have_tree;
+  int yendor_backsteps;
 
   vector<shape> shapes;
   string name;
@@ -397,6 +398,7 @@ EX void load(const string& fname, bool after_sliding IS(false)) {
   c.floor_scale = .5;
   c.have_ph = c.have_line = false;
   c.have_tree = false;
+  c.yendor_backsteps = 0;
   exp_parser ep;
   ep.s = s;
   ld angleunit = 1, distunit = 1, angleofs = 0;
@@ -511,6 +513,10 @@ EX void load(const string& fname, bool after_sliding IS(false)) {
     else if(ep.eat("treestate(")) {
       rulegen::parse_treestate(c, ep);
       }
+    else if(ep.eat("yendor_backsteps(")) {
+      c.yendor_backsteps = ep.iparse();
+      ep.force_eat(")");
+      }
     else if(ep.eat("range(")) {
       c.range = ep.iparse();
       ep.force_eat(")");
diff --git a/expansion.cpp b/expansion.cpp
index ac1cf7ba..efbfa271 100644
--- a/expansion.cpp
+++ b/expansion.cpp
@@ -144,6 +144,7 @@ void expansion_analyzer::preliminary_grouping() {
 
 void expansion_analyzer::reduce_grouping() {
   if(reg3::in_rule()) return;
+  if(currentmap->strict_tree_rules()) return;
   int old_N = N;
   vector<int> grouping;
   grouping.resize(N);
@@ -208,6 +209,7 @@ bignum& expansion_analyzer::get_descendants(int level) {
   }
 
 bignum& expansion_analyzer::get_descendants(int level, int type) {
+  if(!N) preliminary_grouping(), reduce_grouping();
   auto& pd = descendants;
   size_upto(pd, level+1);
   for(int d=0; d<=level; d++)
diff --git a/geometry2.cpp b/geometry2.cpp
index ea0b0019..bb04af1a 100644
--- a/geometry2.cpp
+++ b/geometry2.cpp
@@ -872,6 +872,7 @@ EX pathgen generate_random_path(cellwalker start, int length, bool for_yendor, b
     int t = -1;
     bignum full_id;
     bool onlychild = true;
+    bool launched = false;
 
     cellwalker ycw = start;
     if(for_yendor) setdist(p.path[0], 7, NULL);
@@ -901,6 +902,37 @@ EX pathgen generate_random_path(cellwalker start, int length, bool for_yendor, b
         if(isize(ds)) ycw += ds[hrand(isize(ds))];
         }
 
+      else if(currentmap->strict_tree_rules()) {
+        if(for_yendor && i < arb::current.yendor_backsteps) {
+          println(hlog, i, " < ", arb::current.yendor_backsteps);
+          ycw.spin = 0;
+          }
+
+        else {
+          if(!launched) {
+            t = ycw.at->master->fieldval;
+            bignum b = expansion.get_descendants(length-i, t);
+            p.full_id_0 = full_id = hrand(b);
+            /* it may happen that the subtree dies out */
+            if(!full_id.approx_int()) goto stupid;
+            launched = true;
+            }
+
+          ycw.spin = 0;
+
+          auto& r = rulegen::treestates[t];
+          for(int ri=0; ri<isize(r.rules); ri++) {
+            int tch = r.rules[ri];
+            if(tch < 0) continue;
+            auto& sub_id = expansion.get_descendants(length-1-i, tch);
+            if(full_id < sub_id) {
+              t = tch; ycw += ri; break;
+              }
+            full_id.addmul(sub_id, -1);
+            }
+          }
+        }
+
       else if(trees_known()) {
         auto sdist = [start] (cell *c) { return celldistance(start.at, c); };
         if(i == 0) {
@@ -951,6 +983,7 @@ EX pathgen generate_random_path(cellwalker start, int length, bool for_yendor, b
         }
 
       else {
+        stupid:
         // stupid
         ycw += rev;
         // well, make it a bit more clever on bitruncated a4 grids