box in box by rst76

main=mapM(putStrLn.(s>>=).f 20 8)s
f m d y x|max x y<m-d=f(m-d)(d-2)y x|0<1=["[]","  "]!!min(mod(x+m)d*mod(y+m)d)1
s=map abs[-20..20]

Note that non-ascii characters in the above source code will be escaped (such as \x9f).

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