Comparing single values against a list of values isn't too hard.

use List::Util qw[ min max ];

if( $X < min( $a, $b, $c )
and $Y > max( $a, $b, $c )
or  $Z < min( $b, $c, $d ) 
) {
    # do something
}
[download]

The lists can equally be arrays of as many values as you need.

Unfortunately, the example is incomplete. I couldn't find a state diagram for 'possibly' :)