English
If a TransGen from a to b and a RefTransGen from b to c, then a TransGen from a to c.
Русский
Если имеется TransGen r a b и ReflTransGen r b c, то есть TransGen r a c.
LaTeX
$$$ \forall {α} {r} {a b c : α}, \mathrm{TransGen} r a b \to \mathrm{ReflTransGen} r b c \to \mathrm{TransGen} r a c $$$
Lean4
theorem trans_left (hab : TransGen r a b) (hbc : ReflTransGen r b c) : TransGen r a c := by
induction hbc with
| refl => assumption
| tail _ hcd hac => exact hac.tail hcd