Function prop::imply::or_split_db

pub fn or_split_db<A: Prop, B: DProp, C: Prop>(
    f: Imply<A, Or<B, C>>
) -> Or<Imply<A, B>, Imply<A, C>>

(a => (b ∨ c)) => (a => b) ∨ (a => c).