public void buildMateriiProf() {
		// materia is the key
		for (Materie m : materii) {
			// map is the value
			HashMap<Clasa, Profesor> map = new HashMap<Clasa, Profesor>();
			// seek teachers with corresponding materie
			for (Profesor p : profesori) {
				if (p.getMaterie().equals(m)) {
					// in the classes where they teach
					for (String s : p.getClase()) {
						for (Clasa c : this.getClasa()) {
							if (c.getIdClasa().equals(s)) {
								// if we have found a fitting entry
								// put in dictionary
								map.put(c, p);
							}
						}
					}
				}
			}
			materii_prof.put(m, map);
		}
	}