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add Permutation_filter #305

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Merged
andres-erbsen merged 2 commits into from
Aug 31, 2026
Merged

add Permutation_filter #305

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77179eb
add Permutation_filter
OwenConoly Aug 31, 2026
183e96f
Permutation_filter should be export rather than global
OwenConoly Aug 31, 2026
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11 changes: 11 additions & 0 deletions theories/Sorting/Permutation.v
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Original file line number Diff line number Diff line change
Expand Up @@ -297,6 +297,17 @@ Proof.
inversion_clear HF1; auto.
Qed.

#[export] Instance Permutation_filter (f : A -> bool) :
Proper (@Permutation _ ==> @Permutation _) (filter f).
Proof.
intros l l' H.
induction H; simpl;
repeat match goal with
| |- context[if ?x then _ else _] => destruct x
end;
eauto.
Qed.

Lemma Permutation_Forall2 (P : A -> B -> Prop) :
forall l1 l1' (l2 : list B), Permutation l1 l1' -> Forall2 P l1 l2 ->
exists l2' : list B, Permutation l2 l2' /\ Forall2 P l1' l2'.
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