Backtracking match algorithm

Figure 2 Examples for description of the backtracking match algorithm. (The hydrogen atoms are treated as implicit ones and thus ignored in the procedure.)...

The performance of the original backtracking algorithm can be further improved by pruning-off fruitless branches of a search tree as early as possible. One technique for achieving this was introduced into a backtracking match algorithm by Ullmann in 1976 [16]. 

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