mathlib

710fe040 - feat(model_theory/order): Defines ordered languages and structures (#13088)

feat(model_theory/order): Defines ordered languages and structures (#13088) Defines ordered languages and ordered structures Defines the theories of pre-, partial, and linear orders, shows they are modeled by the respective structures. Co-authored-by: Floris van Doorn <fpvdoorn@gmail.com>