Part $6-$Transmutation

Implement a

positive$-$thinking function, which takes a Tree as argument and produces

a new tree which removes all negative leaves from the original tree. If the

resulting tree would have no nodes, return false.

Hint: the total number of nodes $($leaf and interior$)$ in the resulting tree will be

less than or equal to the total number of nodes in the original, minus the number of

negative leaves in the original.