#### Reading material

Pages 263-265 (Section 6.4.1)
#### Additional material

Implementation of a binary tree by means of an array in
PostScript and
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**Algorithm** isBST(*tree*):

*Input:* a binary tree whose nodes contains keys

*Output:* (Is *tree* a binary search tree?,
minimal key stored in *tree*, maximal key stored in *tree*)

**if** *tree* has one node **then**

*result* (true, key of root of *tree*, key of root of *tree*)

**else**

(*isBST*_{left}, *min*_{left}, *max*_{left})
isBST(left subtree of *tree*)

(*isBST*_{right}, *min*_{right}, *max*_{right})
isBST(right subtree of *tree*)

*isBST*
*isBST*_{left} *isBST*_{right}
*max*_{left} <= key of root of *tree* <= *min*_{right}

*min* min(key of root of *tree*, *min*_{left}, *min*_{right})

*max* min(key of root of *tree*, *max*_{left}, *max*_{right})

*result* (*isBST*, *min*, *max*)

**return** *result*

#### Question

Give the pseudocode for removeAboveExternal in the implementation of a binary tree with an array.