'If ``edge1`` and ``edge2`` have precisely one common endpoint,
returns an edge which would form a triangle with ``edge1`` and
``edge2``.
If ``edge1`` and ``edge2`` don\'t have a common endpoint,
returns ``None``.
If ``edge1`` and ``edge`` are the same edge, returns ``None``.'

@staticmethod
def _juxtapose_edges(edge1, edge2):

    intersection = (edge1 & edge2)
    if (len(intersection) != 1):
        return None
    return ((edge1 - intersection) | (edge2 - intersection))
