@pkw
Interesting but no, this is series:iterate which is a lazily evaluated let form that maps over serieses. It's like
> (ql:Quickload :series)
> (series::install)
> (iterate ((numbers (scan '(1 2 3)))
(more-numbers (scan '(1/2 3/2 4/3))))
(print (+ numbers more-numbers)))
3/2
7/2
13/3
NIL
> (series::install :remove t)