1. C::J N(D), R::E L (B)

   
    if N!=L 	print no relation
    else if C and R are related in inheritance
      if N=L
      	if B and D are related in subtyping AND J and E are related in subtyping
		then print 'overriding combination' (typesafe  or typeunsafe+exceptions)
	else print 'overloading'
      else print 'no relation'

      * in table form

      classes	function name	i/p types 	o/p types 	inference
      related	same		related		related

      no	X		X		X		not related
      yes	X		X		X		not related
      yes	1		0		X		overloading
      yes	1		X		0		overloading
      yes	1		1		1		typesafe or static-unsafe
      								overriding combinations



     overriding combinations wrt
				S1 f(T1)
	   			   ^ 
				S2 f(T2)

     i/p		o/p		static-safe?
     ------------------------------------------------
     down(T1->T2)	up(S1<-S2)	yes			
     down		down(S1->S2)	no, RTTI+exceptions
     up	(T1<-T2)	down		no  RTTI+exceptions
     up			up 		no  RTTI+exceptions
     		
    

2. (a) by calling super class's member functions from inside subclass, by
	using super class's member variables (protected) in subclass.  
   (b) by exporting superclass's member functions as if they are provided
       by subclass. (is_a relation)  
   (c) code written in terms of superclass is reusable across the instances
   	of subclasses through subsumption/polymorhpism.  


3. An example contract

	coin box has: ticket value buttons, coin slot, ticket/coin pickup tray

	member			precondition			postcondition			action if
												precondition is
												violated

	selectTicketValue	Pre1: coin cache >= ticket	ticket printed,			try with Pre2.
				value				change kept in cache,
								ticket value unselect

	selectTicketValue	Pre2: coinbox is adequately	ticket value remembered		empty, cache>=val:	
				empty for needed value  					try with Pre2.
				i.e. selected minus in cache					not empty: flag coinboxfull 
												indicator


	insertCoin		ticket value selected		ticket printed if 
								coin cache >= ticket value,
								change value cached in:ticket
								value unselect

	loadTickets 		... (optional)

   Implementation is expected in Java or C++ with assertions, or in Eiffel with post and 
   preconditions