Reduce

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 what we need to process a result from mapcan:

>(reduce + (mapcat testforz
                   '(z m u l e z r u l e z)))
;                   (1)       (1)       (1)
; = (reduce + '(1 1 1))

3