mathlib

f4e7f82a - chore(model_theory/definability): Change variable order in definability (#12802)

chore(model_theory/definability): Change variable order in definability (#12802) Changes `first_order.language.definable` and `first_order.language.definable_set` to `set.definable` and `set.definable_set`. Makes `set.definable` a `def` rather than a `structure`.