How to draw methods inside self message methods for UML sequence diagrams

Question

I'm trying to draw a sequence diagram for a code which looks like this:

Class Z:
   method y()

Class X:
   method w()

Class A inherits X & Z:
   method b() { 
       calls y()
       calls w()
   }

A a;
a.b()

At first I thought that I should draw a self message method like this:

     ┌─┐         
     │A│         
     └┬┘         
     ┌┴┐         
     │ │────┐    
     │ │    │ b()
     │ │<───┘    
     │ │         
     │ │         
     └┬┘    
     ┌┴┐     
     │A│         
     └─┘                         

but then I realised that this doesn't show how b() calls y(), so I considered this:

     ┌─┐          ┌─┐          ┌─┐
     │A│          │Z│          │X│
     └┬┘          └┬┘          └┬┘
     ┌┴┐    y()    │            │ 
     │ │ ─────────>│            │ 
     │ │           │            │ 
     │ │          w()           │ 
     │ │ ──────────────────────>│ 
     └┬┘           │            │ 
      │         return          │ 
      │<─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ │ 
     ┌┴┐          ┌┴┐          ┌┴┐
     │A│          │Z│          │X│
     └─┘          └─┘          └─┘

But then this one doesn't show b(). Is there a way I can draw this sequence diagram so that I can show both methods?

Answer 1

The call of b seems to be made out of something associated to a class, so let say the initial caller is not important using a found message, then y and w are applied on the instance of A executing b whatever these operations are inherited, so :