sub assemble { $x='';sub a{($p,$q)=@_;return$q if!$p;$l=length$p;for(0..$l){$y= substr($p,0,$_).$q;return$y if substr($y,0,$l)eq$p}}sub b{my$s;$s=a( $s,$_)for@_;$x=$s if!$x||length$s