31 lines
768 B
Text
31 lines
768 B
Text
inductive Weekday where
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| sunday : Weekday
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| monday : Weekday
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| tuesday : Weekday
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| wednesday : Weekday
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| thursday : Weekday
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| friday : Weekday
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| saturday : Weekday
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def Weekday.next : Weekday -> Weekday :=
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fun d => match d with
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| sunday => monday
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| monday => tuesday
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| tuesday => wednesday
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| wednesday => thursday
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| thursday => friday
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| friday => saturday
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| saturday => sunday
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def Weekday.previous : Weekday -> Weekday
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| sunday => saturday
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| monday => sunday
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| tuesday => monday
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| wednesday => tuesday
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| thursday => wednesday
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| friday => thursday
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| saturday => friday
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theorem Weekday.nextOfPrevious (d : Weekday) : next (previous d) = d := by
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cases d
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allGoals rfl
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