main=interact$unlines.f.lines
f t=filter(""/=)[h[lookup(x,80-y)[((x+x+y+y,x-y),c)|(y,s)<-z t,(x,c)<-z s]|x<-n]|y<-n]
h s|all(Nothing==)s=""
h(c:s)=maybe ' 'id c:h s
n=[0..120]
z=zip n
Note that non-ascii characters in the above source code will be escaped (such as \x9f).