2015-01-05 19:49:27 +00:00
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inductive day :=
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monday, tuesday, wednesday, thursday, friday, saturday, sunday
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open day
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2015-02-26 00:20:44 +00:00
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definition next_weekday : day → day
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| next_weekday monday := tuesday
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| next_weekday tuesday := wednesday
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| next_weekday wednesday := thursday
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| next_weekday thursday := friday
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| next_weekday _ := monday
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2015-01-05 19:49:27 +00:00
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theorem next_weekday_monday : next_weekday monday = tuesday := rfl
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theorem next_weekday_tuesday : next_weekday tuesday = wednesday := rfl
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theorem next_weekday_wednesday : next_weekday wednesday = thursday := rfl
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theorem next_weekday_thursday : next_weekday thursday = friday := rfl
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theorem next_weekday_friday : next_weekday friday = monday := rfl
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theorem next_weekday_sat : next_weekday saturday = monday := rfl
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theorem next_weekday_sunday : next_weekday sunday = monday := rfl
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example : next_weekday (next_weekday monday) = wednesday :=
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rfl
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