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This is obtained as follows: Initially, the only matching clause-head for the query is the first one, so proving the query is equivalent to proving the body of that clause with the appropriate variable bindings in place, i. e., the conjunction.
The next goal to be proved is the leftmost one of this conjunction, i. e.,.
Two clause heads match this goal.
The system creates a choice-point and tries the first alternative, whose body is.
This goal can be proved using the fact, so the binding is generated, and the next goal to be proved is the second part of the above conjunction:.
Again, this can be proved by the corresponding fact.
Since all goals could be proved, the query succeeds.
Since the query contained no variables, no bindings are reported to the user.
A query with variables, like:

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