ISBN2 by ksk

#!ruby -p
sub("?"){(0..9).find{|$u|u,_=?u,22
scan(/./){_+=$&.tr("?X","#$u$")[0]*u-=u%5*22-56}
_%(u%7+6)<1}}

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

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