funext n
α : Type
lengths : Stream' ℕ
a : Stream' α
⊢ break_into_words lengths a = fun i => Stream'.take (lengths i) (Stream'.drop (∑ j ∈ Finset.range i, lengths j) a)
case h
α : Type
lengths : Stream' ℕ
a : Stream' α
n : ℕ
⊢ break_into_words lengths a n = Stream'.take (lengths n) (Stream'.drop (∑ j ∈ Finset.range n, lengths j) a)