27 lines
776 B
Text
27 lines
776 B
Text
-- Copyright (c) 2014 Microsoft Corporation. All rights reserved.
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-- Released under Apache 2.0 license as described in the file LICENSE.
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-- Author: Leonardo de Moura
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import logic.decidable logic.inhabited
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open decidable
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inductive unit : Type :=
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star : unit
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namespace unit
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notation `⋆`:max := star
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-- remove duplication?
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protected theorem equal (a b : unit) : a = b :=
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rec (rec rfl b) a
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protected theorem subsingleton [instance] : subsingleton unit :=
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subsingleton.intro (λ a b, equal a b)
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theorem eq_star (a : unit) : a = star :=
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equal a star
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protected definition is_inhabited [instance] : inhabited unit :=
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inhabited.mk ⋆
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protected definition has_decidable_eq [instance] : decidable_eq unit :=
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take (a b : unit), inl (equal a b)
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end unit
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