class Matrix extends Menge<Menge<Integer>> { mul(m){ Menge<Menge<Integer>> ret; ret = new Matrix(); i; i = 0; while(i <size()) { v1; v2; v1 = this.elementAt(i); v2 = new Menge<Integer>(); j; j = 0; ret.addElement(v2); i++; } return ret; } }