English
Equality is an equivalence relation: reflexive, symmetric, and transitive.
Русский
Равенство является эквивалентным отношением: рефлексивно, симметрично и транзитивно.
LaTeX
$$$(\\forall x\\in\\alpha, x=x) \\land (\\forall x,y\\in\\alpha, x=y \\rightarrow y=x) \\land (\\forall x,y,z\\in\\alpha, x=y \\rightarrow y=z \\rightarrow x=z)$$$
Lean4
theorem eq_equivalence {α : Sort*} : Equivalence (@Eq α) :=
⟨Eq.refl, @Eq.symm _, @Eq.trans _⟩
-- These were migrated to Batteries but the `@[simp]` attributes were (mysteriously?) removed.