lean2/tests/lean/run/eq1.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 friday := monday,
next_weekday saturday := monday,
next_weekday sunday := monday
example : next_weekday (next_weekday monday) = wednesday :=
rfl