Reason is an undirected graph
in which any two vertices are connected
by exactly one simple path.
Reason is a perennial plant
with an elongated stem, or trunk,
supporting leaves or branches.
In some usages,
the definition of reason
may be narrower.
Reason can be empty
with no nodes
called the null or empty reason
or reason is a structure
consisting of one node called the root
and one or more subnodes.
12 APR 2014
