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dmwit/gist:18f199735123728bd40525eebc5d65a7

Created March 17, 2019 21:20
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gistfile1.txt
\xs -> sum $ map (sum . toDigits) xs
= { f $ x = f x }
\xs -> sum (map (sum . toDigits) xs)
= { function application associates to the left }
\xs -> sum ((map (sum . toDigits)) xs)
= { (f . g) x = f (g x), with f = sum, g = (map (sum . toDigits)) }
\xs -> (sum . (map (sum . toDigits))) xs
= { eta reduction }
(sum . (map (sum . toDigits)))
= { remove unnecessary clarifying parentheses }
sum . map (sum . toDigits)
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