public void add(ArrayList<Predicate> pl){
		for(int i = 0; i < pl.size(); i++){ // for each predicate
			Predicate p = pl.get(i);
			
			// If the predicate is USED-RAILWAYS
			if(p.getName().equals("USED-RAILWAYS")){
				// We increment or decrement the number of occupied spaces.
				String varName = p.getVariables().get(0).getName();
				switch (varName){
					case "n+1":	this.occupied++;
								break;
					case "n-1":	this.occupied--;
								break;
				}
				
			} else {
			
				boolean found = false;
				int j = 0;
				while(j < predList.size() && !found){
					found = predList.get(j).equalsPredicate(p);
					j++;
				}
				
				// We add it to the predicates list only if it is not already in.
				if(!found){
					predList.add(p);
				}
				
			}
			
		}
	}