#define f() F
#define g(x) Here is x.
/* This introduces a failure that is only 
due to interpreting the "." as a single tokens here, 
but expecting to see ".." as a single token in the other case. */
//#define h(x, y) x and y went down the hill. 
#define h(x, y) x and y went down the hill...
f() is F
g(      )
g()
g(cats and dogs)
h(Jack,Jill)
h(f(),G)
g(h(f(),f()))