It will be convenient to express a discrete pdf as a continuous pdf using
``delta functions''.
This will make the ensuing discussion easier to follow and simplifies many of
the manipulations for discrete pdf's. Given a discrete pdf 
, let
us associate event i with the discrete r.v. 
, and then define an
equivalent
``continuous'' pdf as follows:
Here 
is the ``delta'' function and it satisfies the following
properties:
