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/character/vcharacter.v b/mathcomp/character/vcharacter.v
index 4a113b6..72bacc3 100644
--- a/mathcomp/character/vcharacter.v
+++ b/mathcomp/character/vcharacter.v
@@ -464,7 +464,7 @@ Proof.
 move=> Zphi def_n lt_n_4.
 pose S := [seq '[phi, 'chi_i] *: 'chi_i | i in irr_constt phi].
 have def_phi: phi = \sum_(xi <- S) xi.
-  rewrite big_map /= big_filter big_mkcond {1}[phi]cfun_sum_cfdot.
+  rewrite big_image big_mkcond {1}[phi]cfun_sum_cfdot.
   by apply: eq_bigr => i _; rewrite if_neg; case: eqP => // ->; rewrite scale0r.
 have orthS: orthonormal S.
   apply/orthonormalP; split=> [|_ _ /mapP[i phi_i ->] /mapP[j _ ->]].