DelaunayTriangle n2 = twinTriangle.getNeighbor(i);
if (n1 == null && n2 == null) {
continue;
} else if (n1 != null && n2 != null
&& n1.asTriangleXZ().equals(n2.asTriangleXZ())) {
continue;
} else {
fail(String.format("neighbor %d different: %s vs. %s",
i, n1, n2));
}