mathlib3

7c2ce0c2 - refactor(set_theory/cardinal/basic): redefine `cardinal.is_limit` in terms of `is_succ_limit` (#18523)

refactor(set_theory/cardinal/basic): redefine `cardinal.is_limit` in terms of `is_succ_limit` (#18523) We redefine `cardinal.is_limit x` as `x ≠ 0 ∧ is_succ_limit x`. This will allow us to make use of the extensive `is_succ_limit` API in the future.