IMO -
I think the term "multiple inheritance" is applicable
only for classes and not for interfaces. Here you are
creating a hierarchy of interfaces.
Since c itself is declared as an interface and not
a class, compiler does not apply the multiple inheritance
check here. If you declare c as a class and try to
compile your code, among other error messages is one
which says
Multiple inheritance is not supported.
I hope this substantiates my argument

However, I am very curious to know if creating
such (multiple)inheritance interface hierarchies
is a good design practice. Also, is there any
example for such interface(s)?
Ajith