sub c{@r='';@r=map{$c=$_;map$c.$_,@r}@_ for 1..shift;@r}

sub i{($t=pop)=~s/./.*\Q$&/gs;pop=~/$t/s}

##</code><code>##

sub assemble {
my$n;{for(c($n++,map{split//}@_)){$v=$_;map{i($v,$_)||next}@_;return$_}redo}
}

##</code><code>##

print assemble(qw(oa af wf wa));