ISBN2 by pooq

g=:4 :'I.0=x|(+/b*,"."0 a)+y*i.X'
3 :0;._2(1!:1)3
a=:4}.y
p=:a i.'?'
X=:10
wd({.":".>(X=#a){'X g p{b=:13$1 3';'11 g>:p[b=:>:i.X')(p+4)}y
)

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

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