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# for loop
for my $i (0 .. $#a1) {
...
            if $a2[$j] eq $a1[$i];
    }
}

# schwartzian [sp?] transform (perhaps not a paradigmatic example thou
+gh)
my @indicies = map {$_->[0]}
    grep {$a1[$_->[0]] eq $a2[$_->[1]]}
    map { my $l = $_; (map {[$l,$_]} 0 .. $#a2) } 0 .. $#a2;