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Refuting a pathological but reachable pattern with chess #7822
Original bug ID: 7822
When typing overly complex refutation clauses, it is possible to exploit the lack of backtracking for ident binding time in the counter-example search to go beyond the authorized number of existential variables during the search and then refute the pattern even if counter-examples exist further down in the search tree.
As an illustration, the attached file construct a type level encoding of
Does this count as a bug?
Comment author: @Octachron
On 4.06.1, it takes me ~ 10 minutes to find a counter-example for the first refutable clause. I have another example with a 3×4 board where it only takes ~ 30 seconds to find a counter-example with 4.06.1 (whereas 4.07 still fail to find it). Should I upload it?
Comment author: @garrigue
For there record:
there_are_no_wazir_tours (Right::Right::Up::Up::Left::Down::Left::Up::Left::Down::Down::Down:: Right::Right::Right::);;
Turning it into a segfault should be easy (using the result type).