The function reduce applies a specified function to the first two elements of a list, then to the result of the first two and the third element, and so forth.
>(reduce '+ '(1 2 3 17)) 23 >(reduce '* '(1 2 3 17)) 102
reduce is just what we need to process a result from mapcan:
>(reduce '+ (mapcan 'testforz
'(z m u l e z r u l e z)))
3