Sub-BST: Write a method/function that decides whether a given BST is a sub-BST of another BST. Note that a BST t1 is a sub-BST of t2 iff one of the following holds: key[root[t1]] = key[root[t2]], and left[t1] and right[t1] are sub-BSTs of left[t2] and right[t2], respectively, t1 is a sub-BST of left[t2], or t1 is a sub-BST of right[t2]. Note also that an empty BST (root=nil) is a subBST of any BST.

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