public static Constraint differentialActivity(boolean activating)
	{
		if (activating) return new AND(new MappedConst(new ActivityConstraint(true), 1), new MappedConst(new ActivityConstraint(false), 0));
		else return new AND(new MappedConst(new ActivityConstraint(true), 0), new MappedConst(new ActivityConstraint(false), 1));
	}
public static Constraint differentialActivity ( boolean activating ) { if ( activating ) return new AND ( new MappedConst ( new ActivityConstraint ( true ) , 1 ) , new MappedConst ( new ActivityConstraint ( false ) , 0 ) ) ; else return new AND ( new MappedConst ( new ActivityConstraint ( true ) , 0 ) , new MappedConst ( new ActivityConstraint ( false ) , 1 ) ) ; }
Gets a constraint to ensure that ensures only one of the two PhysicalEntities has an
activity. Size of this constraint is 2.

@param activating true/false (TODO explain)
@return constraint to make sure only one of the PhysicalEntity has an activity