feat: lemmas about List.join #5130
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| theorem join_eq_append (xs : List (List α)) (ys zs : List α) : | ||
| xs.join = ys ++ zs ↔ | ||
| (∃ as bs, xs = as ++ bs ∧ ys = as.join ∧ zs = bs.join) ∨ | ||
| ∃ as bs c cs ds, xs = as ++ (bs ++ c :: cs) :: ds ∧ ys = as.join ++ bs ∧ |
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You could strengthen this by stating that bs is not empty, as else we are in the first case, right?
And maybe more natural to only have a nonempty cs rather than introducing c::cs?
Or if you like this style, use b::bs for the first list?
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