Instance frequencySizeMonotonic_alt :
forall {A : Type} (g0 : G A) (lg : seq (nat * G A)),
SizeMonotonic g0 ->
lg \subset [set x | SizeMonotonic x.2 ] ->
SizeMonotonic (frequency g0 lg).

Lemma pickDrop_subset {A} (l1 l2 : seq (nat * G (option A))) (n m : nat) g :
pickDrop l1 n = (m, g, l2) ->
l2 \subset l1.