'Construct a new ``LeafEdge``.
:param leaf: The new edge\'s leaf value, specifying the word
that is recorded by this edge.
:param index: The new edge\'s index, specifying the position of
the word that is recorded by this edge.'

def __init__(self, leaf, index):

    self._leaf = leaf
    self._index = index
    self._comparison_key = (leaf, index)
