English
From a ∨ (b ∨ c) and implications a→d, b→e, c→f, derive d ∨ (e ∨ f).
Русский
Из a ∨ (b ∨ c) и импликаций a→d, b→e, c→f следует d ∨ (e ∨ f).
LaTeX
$$$a \\lor (b \\lor c) \\to (a \\to d) \\to (b \\to e) \\to (c \\to f) \\to d \\lor (e \\lor f)$$$
Lean4
theorem imp3 {d e c f : Prop} (had : a → d) (hbe : b → e) (hcf : c → f) : a ∨ b ∨ c → d ∨ e ∨ f :=
Or.imp had <| Or.imp hbe hcf