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by falsissime
1258 days ago
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Just to note one error in I.2.1: > ... whereas unification without the occur check is linear on the
size of the smallest of the terms being unified. This claim is incorrect, it goes far beyond what is possible. To see its incorrectness consider the unification problem X = Y. And just for illustrative purposes, think of them both as being very big and evolved. Now, consider a related unification problem Z-Z = X-Y with Z just a variable. According to above claim, the cost would be now independent of X and Y which cannot be. |
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I wonder if all that was more of a consideration in an older time, with weaker hardware. Anyway where I come from (ILP research, again) "polynomial time" is synonymous to "efficient" and the bigger problem is proofs failing to terminate.
I might actually try some learning experiments with the occurs check flag set to "true" just to see what happens. I mean, I wonder. I'm so used to leaving the flag to default false that I wonder if I haven't formed a completely wrong model about the execution of Prolog programs. I've been coding in Prolog for more than ten years now and it still catches me off-guard at times.