English
If a relation holds between a and b and b is connected to c by a reflexive-transitive closure, then a to c is a TransGen relation.
Русский
Если r a b и b связан с c через ReflTransGen, то TransGen r a c.
LaTeX
$$$ ∀ {α} {r} {a b c : α}, r a b \to \mathrm{ReflTransGen} r b c \to \mathrm{TransGen} r a c $$$
Lean4
theorem head' (hab : r a b) (hbc : ReflTransGen r b c) : TransGen r a c :=
trans_left (single hab) hbc