Upside down

upsidedown.lhs

#!/usr/bin/env runhaskell

> import Data.Char (toLower)

Once @malfet wrote: uʍop ǝpısdn ǝʇıɹʍ oʇ pǝsn ǝq uɐɔ sloqɯʎs sɔıʇǝuoɥd.

Indeed, there are upside-down pairs for most of the lower-case letters.
Only 'j' is a problem.

> abc = [ ('a', 'ɐ'), ('b', 'q'), ('c', 'ɔ'), ('d', 'p'), ('e', 'ə')
>       , ('f', 'ɟ'), ('g', 'ɓ'), ('h', 'ɥ'), ('i', 'ᴉ'), ('j', 'f')
>       , ('k', 'ʞ'), ('l', 'ʅ'), ('m', 'ɯ'), ('n', 'u'), ('o', 'o')
>       , ('p', 'd'), ('q', 'b'), ('r', 'ɹ'), ('s', 's'), ('t', 'ʇ')
>       , ('u', 'n'), ('v', 'ʌ'), ('w', 'ʍ'), ('x', 'x'), ('y', 'ʎ')
>       , ('z', 'z') ]

So let's make a unix filter out of this alphabet:

> main = interact $ unlines .
>   map (map ((\c -> maybe c id (lookup c abc)) . toLower) . reverse) .
>   reverse . lines