Backtracking in ordinary depth-first search is called chronological backtracking because decisions are retracted and changed according to the order in which they were made, with the most recent decision being changed first.
In some domains this is appropriate, since there is a time dependency between actions. In chess, for example, moves must be made in order.
Other domains, however, do not have this restriction.
Example: graph isomorphism: find a one-to-one, onto mapping between vertices of one graph and vertices of another that preserves connectivity. Vertices can be chosen in any order.
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