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

##</code><code>##

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

##</code><code>##

    ~0000 & 0101 ) =~ tr[$ndiff][$ndiff]

##</code><code>##

    ~$string1 & $string2 ) =~ tr[\1][\1]