code: public int getID(Variable var) {
  		Variable[] vars = this.getVariables();
  		for (int i = 0; i < vars.length; i++) {
  			if (vars[i].equals(var)) return i;
  		}
  		return -1;
  	}
docs: Get the ID of a {@link Variable}.
  @param var The {@link Variable} of which to get the ID.
  @return The ID of the given variable.