Examples of two useful predicates

Two of DW's most useful predicates are assign(A,B,C) and call(A,B,C).
Here's a good rundown I was given on how to use them.

Given the following code example
c = a.lookup()

we have call(A,B,C) where A is a.lookup(), B is lookup() and C is a
and assign(A,B,C) where A is c = X (where X is the return value of a.lookup), B is c and C is a.lookup()