use incident_edges instead of neighbours for correct fusion in basicr…

…ules.py

pyzx/basicrules.py

@@ -204,9 +204,12 @@ def fuse(g: BaseGraph[VT,ET], v1: VT, v2: VT) -> bool:
         set_z_box_label(g, v1, get_z_box_label(g, v1) * get_z_box_label(g, v2))
     else:
         g.add_to_phase(v1, g.phase(v2))
-    for v3 in g.neighbors(v2):
-        if v3 != v1:
-            g.add_edge((v1,v3), edgetype=g.edge_type(g.edge(v2,v3)))
+    for e in g.incident_edges(v2):
+        source, target = g.edge_st(e)
+        other_vertex = source if source != v2 else target
+        if other_vertex == v1 and g.edge_type(e) == EdgeType.SIMPLE:
+            continue
+        g.add_edge((v1,other_vertex), edgetype=g.edge_type(e))
     g.remove_vertex(v2)
     return True
 

pyzx/rules.py

@@ -225,8 +225,8 @@ def spider(g: BaseGraph[VT,ET], matches: List[MatchSpiderType[VT]]) -> RewriteOu
 
         # edges from the second vertex are transferred to the first
         for e in g.incident_edges(v1):
-            edge_st = g.edge_st(e)
-            other_vertex = edge_st[0] if edge_st[1] == v1 else edge_st[1]
+            source, target = g.edge_st(e)
+            other_vertex = source if source != v1 else target
             new_e = (v0, other_vertex)
             if new_e not in etab: etab[new_e] = [0,0]
             etab[new_e][g.edge_type(e)-1] += 1