Exercice given at the end of Leure.
By definition, a forewithk trees is a sequence (t, . . . ,tk) ofktrees. Denote byFn(k) the set of all fores withktrees andnvertices. Find a formula for|Fn(k)|.
Hint. Extend the bijeion between trees of sizenandS()n to a bijeion betweenFn(k)andS(k)n .