full parenthesization of n+1 factors ((ab)c)d (a(bc))d (ab)(cd)a((bc)d)a(b(cd)) full binary trees with n+1 leaves 心公公 full binary trees with n+1 leaves ((ab)c)d (a(bc))d (ab)(cd) a((bc)d) a(b(cd)) full parenthesization of n+1 factors