1) Recall from Definition 5.16 that we defined abinary tree as

1. an empty tree, denoted by null; or
2. aroot node x, aleft subtree T, and aright subtree T_r, wherex is an arbitrary value andT andT_r are both binary trees.

A heap is a binary tree where each node stores a priority, and in which every node satisfies the heap property:the priority of a node u must be greater than or equal to the priorities of the roots of both of u's subtrees. (The restriction only applies for a subtree that is not null.)