a=*$< f=proc{|x,y|(putc C;f[x,f[x,f[x-1,f[x+1,S[x]=y]]+1]-2])if(S=a[y])&&32<C=S[x];y} f[0,0]

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

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