Base step: When h = 0, there is only one node in the tree and it is a leaf. This is correct because leaves(0) = 20 = 1.
Inductive Hypothesis: Assume leaves(h-1) = 2h-1
Inductive Step: Each of the leaves in a tree of height h-1 can have 2 children, so:
| leaves(h) | = 2 × leaves(h-1) | |
| = 2 × 2h-1 | by the I. H. | |
| = 2h |