if(currentTutor == null) {
						throw new ShellError("Error! no tutor exists");
					} else if(commandSplit[1].matches("\\d+")) {
						throw new ShellError("Error! a name doesn't have number(s)");
					} else if(!commandSplit[2].matches("\\d+")) {
						throw new ShellError("Error! a matnr. doesn't have letter(s)");
					} else if(prakto.findStudent(Integer.parseInt(commandSplit[2])) != null) {
						throw new ShellError("Error! a student with matnr. " + commandSplit[2] + " already exists");
					} else {
					  	prakto.addStudent(commandSplit[1], Integer.parseInt(commandSplit[2]), currentTutor);
					}
				} catch (ShellError e) {
						System.out.println(e.getMessage());
				}