srecord noeq G22MeshMapper_v2(G22Mesh mesh1, G22Mesh mesh2) {
  // import the important classes
  delegate Anchor, Curve to G22Mesh.
  
  G22MeshMapping mm;
  
  // index structures
  
  MultiMap<Int, Anchor> anchorsByArity2;
    
  // EXCEPTIONS (e.g. meshes don't match in signature)
  
  // set to the reason why when a mapping is deemed impossible
  settable O rejectedBecause;
  
  bool rejected() { ret rejectedBecause != null; }
  
  // INTERNAL VARS
  
  bool prechecksDone;
  S sig1, sig2;
  
  G22MeshMapping get() { ret mm; }
  
  void search_step1() {
    prechecks(); if (rejected()) ret;
    
    // make empty mapping
    mm = new G22MeshMapping(mesh1, mesh2);
    
    anchorsByArity2 = multiMapIndex(mesh2.anchors(), a -> a.arity());
    
    Anchor anchor1 = random(mesh1.anchors());
    Anchor anchor2 = random(anchorsByArity2.get(anchor1.arity());
    mapAnchor(anchor1, anchor2);
  }
  
  bool search_step2() {
    bool change;
    for (curve1 : mesh1.curves()) {
      // skip if curve is already mapped
      if (mm.isMapped(curve1))
        continue with print("Curve is mapped: " + curve1);
      
      // check if anchors are mapped
      Anchor start2 = mm.get(curve1.start);
      Anchor end2 = mm.get(curve1.end);
      
      // If neither anchor is mapped, postpone this curve
      if (start2 == null || end2 == null)
        continue with print("Curve is not discovered yet: " + curve1);
      
      // Start at the mapped anchor, choose a viable curve in mesh2 to map to
      bool startAtEnd = end2 != null;
      Anchor a1other = curve1.anchor(!startAtEnd);
      Anchor a2 = mm.get(curve1.anchor(startAtEnd));
      
      new L<Curve> possibleCurves;
      for (c2 : a2.curves()) {
        if (mm.isMapped(c2)) continue;
        
        // check for arity match
        Anchor a3 = c2.anchorOpposite(a2);
        if (a3.arity() != a1other.arity())
          continue;
          
        // This curve is viable as a mapping target
        possibleCurves.add(c2);
      }
      
      print("Possible curves to map " + curve1 + " to: " + possibleCurves);
      if (empty(possibleCurves))
        ret false with rejectedBecause("Could not map curve " + curve1);
        
      // Map the curve
      Curve c2 = random(possibleCurves);
      bool flipped = c2.start() != a2;
      print("Mapping curve " + curve1 + " to " + c2);
      mm.mapCurve(curve1, c2, flipped);
      set change;
    }
    
    ret change;
  }
  
  void mapAnchor(Anchor anchor1, Anchor anchor2) {
    mm.mapAnchor(anchor1, anchor2);
  }
  
  protected void prechecks {
    set prechecksDone;
    sig1 = mesh1.signature();
    sig2 = mesh1.signature();
    if (!eq(sig1, sig2))
      ret with rejectedBecause(G22SignatureMismatch(mesh1, mesh2));
  }
}