Method trace commented as there is no Event interface
*First implementation of method 'step' for 1 parameter added
*First implementation of method 'end' added
*Interface 'Monitor' turned into an abstract class
*Event representation changed from 'Event' to integer
*New methods 'step' added from 1 to 5 parameters
*Abstract method 'end' added
*Method 'trace' deleted
*Method 'isStateFinal' added