Simplified Common Lisp reference
Symbol class: Conses, Lists and related functions
Symbol type: function
mapcfnlists(one or more) => the first list from lists argument
Argument description:
fn function that takes as many arguments as there are lists
lists lists which elements are processed in parallel

MAPC applies function FN to elements of lists with same index. Each application result forgotten. Elemnts are processed only up to length of the shortest list argument. See MAPCAR, MAPCAN, MAPCON, DOLIST.

(setq dummy nil) =>  NIL
(mapc #'(lambda (&rest x) (setq dummy (append dummy x)))
      '(1 2 3 4)
      '(a b c d e)
      '(x y z)) =>  (1 2 3 4)
dummy => (1 A X 2 B Y 3 C Z)
Function indexFull documentation for mapc (HyperSpec)