lean2/tests/lean/run/eq11.lean

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inductive day :=
monday, tuesday, wednesday, thursday, friday, saturday, sunday
open day
definition next_weekday : day → day,
next_weekday monday := tuesday,
next_weekday tuesday := wednesday,
next_weekday wednesday := thursday,
next_weekday thursday := friday,
next_weekday _ := monday
theorem next_weekday_monday : next_weekday monday = tuesday := rfl
theorem next_weekday_tuesday : next_weekday tuesday = wednesday := rfl
theorem next_weekday_wednesday : next_weekday wednesday = thursday := rfl
theorem next_weekday_thursday : next_weekday thursday = friday := rfl
theorem next_weekday_friday : next_weekday friday = monday := rfl
theorem next_weekday_sat : next_weekday saturday = monday := rfl
theorem next_weekday_sunday : next_weekday sunday = monday := rfl
example : next_weekday (next_weekday monday) = wednesday :=
rfl