lemma drops_fwd_lw: ∀b,f,L1,L2. ⬇*[b, f] L1 ≡ L2 → ♯{L2} ≤ ♯{L1}.
#b #f #L1 #L2 #H elim H -f -L1 -L2 //
[ /2 width=3 by transitive_le/
lemma drops_fwd_lw: ∀b,f,L1,L2. ⬇*[b, f] L1 ≡ L2 → ♯{L2} ≤ ♯{L1}.
#b #f #L1 #L2 #H elim H -f -L1 -L2 //
[ /2 width=3 by transitive_le/