Are duplicate keys allowed in the definition of binary search trees?

Question

I\'m trying to find the definition of a binary search tree and I keep finding different definitions everywhere.

Some say that for any given subtree the left child k

Answer 1

The elements ordering relation <= is a total order so the relation must be reflexive but commonly a binary search tree (aka BST) is a tree without duplicates.

Otherwise if there are duplicates you need run twice or more the same function of deletion!