and
with labels on the nodes.
and
. An embedding from
T'
to
T
is an injective
function from the nodes of
T'
to the nodes of
T
that preserves labels
and ancestorship. Note that since fathership does not need to be preserved,
T'
does not need to be an ordinary subtree.
, where
n
is the number of nodes in the trees
[
156
].
Viggo Kann