lean2/library/standard/data/sum.lean

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-- Copyright (c) 2014 Microsoft Corporation. All rights reserved.
-- Released under Apache 2.0 license as described in the file LICENSE.
-- Author: Leonardo de Moura
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import logic.connectives.prop

namespace sum
inductive sum (A B : Type) : Type :=
| inl : A → sum A B
| inr : B → sum A B

infixr `+`:25 := sum

theorem induction_on {A B : Type} {C : Prop} (s : A + B) (H1 : A → C) (H2 : B → C) : C :=
sum_rec H1 H2 s
end sum