10 lines
317 B
Text
10 lines
317 B
Text
module
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open List
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set_option grind.debug true in
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theorem getLast_getLast_eq_getLast_flatten {l : List (List α)}
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(hl : l ≠ []) (hl' : l.getLast hl ≠ []) :
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(l.getLast hl).getLast hl' =
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l.flatten.getLast (flatten_ne_nil_iff.2 ⟨_, getLast_mem hl, hl'⟩) := by
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cases eq_nil_or_concat l with grind
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