( append [ list? list ] ... ) ⟹ list? ( append [ list? list ] ... obj ) ⟹ *
append, append! append returns a list consisting of the elements of list1 followed by the elements of the other list parameters. The resulting list is always newly allocated, except that it shares structure with the final listi argument. This last argument may be any value at all; an improper list results if it is not a proper list. All other arguments must be proper lists. append! is the "linear-update" variant of append -- it is allowed, but not required, to alter cons cells in the argument lists to construct the result list. The last argument is never altered; the result list shares structure with this parameter.