Listing 6 is_leap_year

function is_leap_year 
{
    integer Y=$1

    if ( (( $((Y%4)) == 0 )) && (( $((Y%100)) != 0 )) ) \
    || (( $((Y%400)) == 0 ))
    then
        return 0
    else
        return 1
    fi
}

# End Listing 6