mathlib3

607f4f8a - feat(model_theory/semantics): A simp lemma for `Theory.model` (#13117)

feat(model_theory/semantics): A simp lemma for `Theory.model` (#13117) Defines `Theory.model_iff` to make it easier to show when a structure models a theory. Co-authored-by: Aaron Anderson <65780815+awainverse@users.noreply.github.com>