lean-lib Build: Features traversable type class (util.data.traversable) cardinality type classes for types with a finite number of values and countably many values (util.data.finite, util.data.countable) category type class (util.category) tactics for proving efficiently inequalities between large literal numbers (util.data.norm_num) machinery for defining coinductive data types (util.data.coinductive) monad for expressing non-terminating computations (util.control.monad.non_terminating, now redundant with mathlib) Various lemmas complementary to the basic libraries