theorem drops_trans: ∀L,L2,s,cs2. ⬇*[s, cs2] L ≡ L2 → ∀L1,cs1. ⬇*[s, cs1] L1 ≡ L →
⬇*[s, cs2 @@ cs1] L1 ≡ L2.
#L #L2 #s #cs2 #H elim H -L -L2 -cs2 /3 width=3 by drops_cons/
theorem drops_trans: ∀L,L2,s,cs2. ⬇*[s, cs2] L ≡ L2 → ∀L1,cs1. ⬇*[s, cs1] L1 ≡ L →
⬇*[s, cs2 @@ cs1] L1 ≡ L2.
#L #L2 #s #cs2 #H elim H -L -L2 -cs2 /3 width=3 by drops_cons/