Suppose that we have formulas:[Backward chaining only works for
Horn clauses, which have at most one positive literal.]
A &and B &rarr C
C &and D &rarr E
A conclusion E can be proved recursively:
In this example, we would know that E is true if we knew that C and D were true; we would know that C is true if we knew A and B ; A and B are in the database, so C must be true; and D is in the database, so E is true.
With careful implementation, backchaining can run in linear time.
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