Problem
Given a proper binary tree T, define the reflection of T to be the binary tree T ′ such that each node v in T is also in T ′, but the left child of v in T is v's right child in T ′ and the right child of v in T is v's left child in T ′. Show that a preorder traversal of a proper binary tree T is the same as the postorder traversal of T ′s reflection, but in reverse order.