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

MAPCON applies function FN to the successive cdr of lists. Each application result is DESTRUCTIVELY concatenated into resulting list. In case of FN results that are fresh lists (non-sharing), the result is same as with (APPLY #'APPEND (MAPLIST ...)). See MAPCAR, MAPCAN, MAPCON, MAP, MAPC.

(mapcon (lambda (x) (list 'start x 'end)) '(1 2 3 4))
=> (START (1 2 3 4) END START (2 3 4) END START (3 4) END START (4) END)
Function indexFull documentation for mapcon (HyperSpec)