Given a vertex "ab1" that is shared between the two loops, return true if
the two associated wedges (a0, ab1, b2) and (b0, ab1, b2) are equivalent
to an edge crossing. The loop relation is also allowed to maintain its
own internal state, and can return true if it observes any sequence of
wedges that are equivalent to an edge crossing.
Given a vertex "ab1" that is shared between the two loops, return true if the two associated wedges (a0, ab1, b2) and (b0, ab1, b2) are equivalent to an edge crossing. The loop relation is also allowed to maintain its own internal state, and can return true if it observes any sequence of wedges that are equivalent to an edge crossing.