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