       else
         [a, b] = stack.first()
         if T.mustFlip a, b
-          c = T.third b, a
+          c = T.third a, b
           recur -> doFlips flip(T, a, b), seq([a,c], [c,b]).concat stack.rest()
         else
           recur -> doFlips T, stack.rest()

      else if x = seq([a, b], [b, c], [c, a]).find((e) => @third__.get(e)?)
        [f, g] = x
        h = @third__.get x
        throw new Error "Orientation mismatch: #{[a,b,c]} <=> #{[f,g,h]}."
      else
        new Triangulation(
          @triangles__.plus(tri(a, b, c)),

        if t.mustFlip r, s
          console.log "Delaunay condition fails for #{u},#{v},#{w},#{x})", ->

#test()
