diff --git a/rogueviz/subquotient.cpp b/rogueviz/subquotient.cpp
new file mode 100644
index 00000000..b2817d01
--- /dev/null
+++ b/rogueviz/subquotient.cpp
@@ -0,0 +1,177 @@
+#include "../hyper.h"
+#include <iostream>
+#include <fstream>
+#include <thread>
+
+namespace hr {
+
+namespace subquotient {
+
+eGeometry gSubquotient(eGeometry(-1));
+
+vector<int> connections;
+
+void create_subquotient(int qty = -1, int id = 0) {
+  start_game();
+  auto ac = currentmap->allcells();
+  auto ca = currentmap->gamestart();
+  
+  for(auto cb: ac) for(int i=0; i<cb->type; i++) for(int m=0; m<2; m++) {
+    vector<cell*> visited;
+    map<cell*, cellwalker> vmap;
+    
+    auto visit = [&] (cell *da, cellwalker db) { 
+      if(vmap.count(da)) {
+        // println(hlog, da, " -> ", db, " [old]");
+        return;
+        }
+      // println(hlog, da, " -> ", db, " [new]");
+      vmap[da] = db;
+      visited.emplace_back(da); 
+      };
+    
+    visit(ca, cellwalker(cb, i, m));
+    
+    for(int i=0; i<isize(visited); i++) {
+      for(int j=0; j<visited[i]->type; j++) {
+        cellwalker wa(visited[i], 0);
+        cellwalker wb(vmap[visited[i]]);
+        wa += j;
+        wb += j;
+        wa += wstep;
+        wb += wstep;
+        int r = wa.spin;
+        wa -= r;
+        wb -= r;
+        // println(hlog, wa, " -> ", wb);
+        setdist(wa.at, 7, nullptr);
+        wa.at->item = itGold;
+        visit(wa.at, wb);
+        }
+      }
+    
+    int vertex = 0, edge = 0, badcycle = 0;
+
+    map<int, int> by_cycle;
+    
+    for(auto [s, wb]: vmap) {
+      if(s == wb.at) { vertex++; continue; }
+      bool is_edge = false;
+      for(int j=0; j<s->type; j++) if(s->move(j) == wb.at && (wb+j).peek() == s)
+        is_edge = true;
+      if(is_edge) { edge++; continue; }
+      int cs = 0;
+      cell *sx = s;
+      auto cw = cellwalker(s, 0);
+      vector<cell*> lst;
+      do {
+        int sp = cw.spin;
+        bool mirr = cw.mirrored;
+        if(cw.mirrored) sp = -sp;
+        cw -= sp;
+        lst.push_back(sx);
+        cw = vmap[sx];
+        if(mirr) cw += wmirror;
+        sx = cw.at;
+        cw += sp;
+        cs++;
+        if(cs >= 100) break;
+        }
+      while(sx != s);
+      if(cw.spin) badcycle++;
+      by_cycle[cs]++;      
+      }
+    
+    if(vertex || edge || badcycle || m == 0) continue;
+    
+    vector<pair<int, int>> bcp;
+    for(auto b: by_cycle) bcp.push_back(b);
+    
+    if(qty == -1)
+      println(hlog, "m=", m, " vertex/edge = ", tie(vertex, edge), " badcycle = ", badcycle, " by_cycle = ", bcp);
+    
+    if(by_cycle[qty] == isize(vmap)) {
+      if(id > 0) {id--; continue; }
+      
+      map<cell*, int> ids;
+      int next_id = 0;
+      vector<cell*> by_id;
+      
+      set<cell*> visited;
+      
+      for(auto s: ac) if(!visited.count(s)) {
+        by_id.push_back(s);
+        ids[s] = next_id;
+        auto sx = s;
+        do {
+          visited.insert(sx);
+          sx = vmap[sx].at;
+          }
+        while(sx != s);
+        next_id++;
+        }
+
+      println(hlog, "ids = ", next_id);
+      connections.clear();
+      if(int(gSubquotient) == -1) {
+        ginf.push_back(ginf[geometry]);
+        gSubquotient = eGeometry(isize(ginf) - 1);        
+        }
+      
+      ginf[gSubquotient] = ginf[geometry];
+      /* we need to be 'pure', unrectified may not work */
+      if(UNRECTIFIED) swap(ginf[gSubquotient].sides, ginf[gSubquotient].vertex);
+      
+      for(int i=0; i<next_id; i++) {
+        cell *s = by_id[i];
+        for(int j=0; j<s->type; j++) {
+          cellwalker cw(s, j);
+          cw += wstep;
+          int res;
+          while(!ids.count(cw.at)) {
+            int sp = cw.spin;
+            bool flip = cw.mirrored;
+            if(flip) sp = -sp;
+            cw -= sp;
+            if(cw.spin) println(hlog, "bad spin");
+            cw = vmap[cw.at];
+            if(flip) cw += wmirror;
+            cw += sp;            
+            }
+          res = ids[cw.at] * s->type + cw.spin;
+          if(cw.mirrored)  res |= quotientspace::symmask;
+          connections.push_back(res);
+          }
+        }
+      
+      stop_game();
+      set_geometry(gSubquotient);
+      variation = eVariation::pure;
+      println(hlog, "variation = ", int(variation));
+      start_game();
+      println(hlog, "started");
+      return;
+      }
+    }
+  }
+
+int readArgs() {
+  using namespace arg;
+           
+  if(0) ;
+  else if(argis("-subquotient")) { start_game(); shift(); create_subquotient(argi()); }
+
+  else return 1;
+  return 0;
+  }
+
+auto fundamentalhook = addHook(hooks_args, 100, readArgs)
+  + addHook(hooks_newmap, 0, [] {
+    if(geometry == gSubquotient) 
+      return (hrmap*) new quotientspace::hrmap_quotient(connections);
+    return (hrmap*) nullptr;
+  });
+
+}
+
+}
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