public void reduceThis(){
		if (elements==null || elements.isEmpty())
			throw new AssertionError("Can't reduce this environment");
		elements.remove(elements.size()-1);
	}
public void reduceThis ( ) { if ( elements == null || elements . isEmpty ( ) ) throw new AssertionError ( "Can't reduce this environment" ) ; elements . remove ( elements . size ( ) - 1 ) ; }
Reduces current environment. Modifies current object, hence NOT THREADSAFE.