7 lines
281 B
Text
7 lines
281 B
Text
module
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namespace List
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-- Should not panic
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#guard_msgs (drop error) in
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theorem countP_filterMap' {p : β → Bool} {f : α → Option β} {l : List α} :
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countP p (filterMap f l) = countP (fun a => ((f a).map p).getD false) l := by
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induction l with grind [=_ Option.getD_map]
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