( eval "( \$string1 | \$string2 )  =~ tr[$n1][$n1]" ),
            ( eval "( ~\$string1 & \$string2 ) =~ tr[\\$ndiff][\\$ndiff]" ),
            ( eval "( \$string1 & ~\$string2 ) =~ tr[\\$ndiff][\\$ndiff]" ),
            ( eval "( \$string1 & \$string2 )  =~ tr[$n2][$n2]" ) ),