algebra ======= Algebraic structures. * [function](function.lean) * [relation](relation.lean) * [binary](binary.lean) : binary operations * [wf](wf.lean) : well-founded relations * [group](group.lean) * [group_power](group_power.lean) : nat and int powers * [group_bigops](group_bigops.lean) : finite products and sums * [ring](ring.lean) * [ordered_group](ordered_group.lean) * [ordered_ring](ordered_ring.lean) * [field](field.lean) * [ordered_field](ordered_field.lean) * [category](category/category.md) : category theory