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diff --git a/doc/changelog/06-ssreflect/10022-ssr-under-setoid.rst b/doc/changelog/06-ssreflect/10022-ssr-under-setoid.rst new file mode 100644 index 0000000000..5e005742fd --- /dev/null +++ b/doc/changelog/06-ssreflect/10022-ssr-under-setoid.rst @@ -0,0 +1,28 @@ +- Generalize tactics :tacn:`under` and :tacn:`over` for any registered + relation. More precisely, assume the given context lemma has type + `forall f1 f2, .. -> (forall i, R1 (f1 i) (f2 i)) -> R2 f1 f2`. The + first step performed by :tacn:`under` (since Coq 8.10) amounts to + calling the tactic :tacn:`rewrite <rewrite (ssreflect)>`, which + itself relies on :tacn:`setoid_rewrite` if need be. So this step was + already compatible with a double implication or setoid equality for + the conclusion head symbol `R2`. But a further step consists in + tagging the generated subgoal `R1 (f1 i) (?f2 i)` to protect it from + unwanted evar instantiation, and get `Under_rel _ R1 (f1 i) (?f2 i)` + that is displayed as ``'Under[ f1 i ]``. In Coq 8.10, this second + (convenience) step was only performed when `R1` was Leibniz' `eq` or + `iff`. Now, it is also performed for any relation `R1` which has a + ``RewriteRelation`` instance (a `RelationClasses.Reflexive` instance + being also needed so :tacn:`over` can discharge the ``'Under[ _ ]`` + goal by instantiating the hidden evar.) Also, it is now possible to + manipulate `Under_rel _ R1 (f1 i) (?f2 i)` subgoals directly if `R1` + is a `PreOrder` relation or so, thanks to extra instances proving + that `Under_rel` preserves the properties of the `R1` relation. + These two features generalizing support for setoid-like relations is + enabled as soon as we do both ``Require Import ssreflect.`` and + ``Require Setoid.`` Finally, a rewrite rule ``UnderE`` has been + added if one wants to "unprotect" the evar, and instantiate it + manually with another rule than reflexivity (i.e., without using the + :tacn:`over` tactic nor the ``over`` rewrite rule). See also Section + :ref:`under_ssr` (`#10022 <https://github.com/coq/coq/pull/10022>`_, + by Erik Martin-Dorel, with suggestions and review by Enrico Tassi + and Cyril Cohen). |