In
graph theory, a
star Sk is the
complete bipartite graph K1,k: a
tree with one internal node and
k leaves (but, no internal nodes and
k + 1 leaves when
k = 1). Alternatively, some authors define
Sk to be the tree of
order k with maximum
diameter 2; in which case a star of
k > 2 has
k - 1 leaves.