I'm not certain you have the General Rules in the correct order - GR2
should happen after GR3, and suchlike.

Also, I suspect that all Items have three different values of dirt,
which need to be combined in various ways. In C++:

class Item {
	private: // Humans cannot distinguish between types of dirt.
		dirt required; // Dirt level required to satisfy human it is "clean".
		dirt intrinsic; // Perceived intrinsic dirt level. Not actual dirt.
Mostly class dependant, but may be affected by prior mould colonies, use
in a student flat, being left somewhere for several weeks, etc.
		dirt extrinsic; // Actual dirt. (And mould colonies).
	
	public:
		bool dirtier( Item const & i ) const { // Note that it is const -
staring at items deciding which is worse does not make them cleaner.
			dirt total_left = required - ( extrinsic + intrinsic );
			dirt total_right = i.required - ( i.extrinsic + i.intrinsic );
			if( total_left > total_right ) {
				return true;
			} else if( total_left < total_right ) {
				return false;
			}
			total_left += extrinsic;
			total_right += i.extrinsic;
			if( total_left > total_right ) {
				return true;
			} else if( total_left < total_right ) {
				return false;
			}
			return required < i.required;
		}
		
		bool should_throw() const { // Again, const - No point cleaning
something you'll be throwing away anyway.
			return intrinsic > required;
		}
};	

Hope this helps solve the ordering problem and the Great Wash Up Or
Throw Away issue (O'Brien, 1999).

Dave.
--
Yes, I must be bored.