Let the points P and Q be the points that belong to all 3 or 4 tiles in a surrounding patch.
The left path from Q to P is congruent to a part p of the right path PQ. In V-tiles of type 1a, P or Q is an element of p. We choosed P∈p in chapters about type 1a and used the name Z instead of P.
In V-tiles of type 1b, neither P nor Q is an element of p. In the graphic the left path QP is congruent to the path WP₁. Rotate the path WP₁ around Z by the angle ε to obtain the left part of PQ.
Opposite to type a, the center Z of rotations by ε is not a point on the boundary of type 1b tiles.