Explicit `bigop` enumeration handling

Added lemmas `big_enum_cond`, `big_enum` and `big_enumP` to handle more
explicitly big ops iterating over explicit enumerations in a `finType`.
   The previous practice was to rely on the convertibility between
`enum A` and `filter A (index_enum T)`, sometimes explicitly via the
`filter_index_enum` equality, more often than not implicitly.
  Both are likely to fail after the integration of `finmap`, as the
`choiceType` theory can’t guarantee that the order in selected
enumerations is consistent.
  For this reason `big_enum` and the related (but currently unused)
`big_image` lemmas are restricted to the abelian case. The `big_enumP`
lemma can be used to handle enumerations in the non-abelian case, as
explained in the `bigop.v` internal documentation.
  The Changelog entry enjoins clients to stop relying on either
`filter_index_enum` and convertibility (though this PR still provides
both), and warns about the restriction of the `big_image` lemma set to
the abelian case, as it it a possible source of incompatibility.

1 files changed, 1 insertions, 1 deletions

diff --git a/mathcomp/algebra/vector.v b/mathcomp/algebra/vector.v
index 87ca0f4..1f8ad30 100644
--- a/mathcomp/algebra/vector.v
+++ b/mathcomp/algebra/vector.v
@@ -1879,7 +1879,7 @@ Variable (K : fieldType) (vT : vectType K).
 Lemma sumv_pi_sum (I : finType) (P : pred I) Vs v (V : {vspace vT})
                   (defV : V = (\sum_(i | P i) Vs i)%VS) :
   v \in V -> \sum_(i | P i) sumv_pi_for defV i v = v :> vT.
-Proof. by apply: sumv_pi_uniq_sum; apply: enum_uniq. Qed.
+Proof. by apply: sumv_pi_uniq_sum; have [e _ []] := big_enumP. Qed.
 
 Lemma sumv_pi_nat_sum m n (P : pred nat) Vs v (V : {vspace vT})
                       (defV : V = (\sum_(m <= i < n | P i) Vs i)%VS) :