string-append takes two arguments, which are both
strings (if the guard is to be met), and returns a string obtained
concatenating together the characters in the first string followed
by those in the second. See concatenate.
Major Section: PROGRAMMING
NOTE: It is probably more efficient to use the Common Lisp function
concatenate in place of string-append. That is,
(string-append str1 str2)is equal to
(concatenate 'string str1 str2).
At any rate, string-append takes two arguments, which are both
strings (if the guard is to be met), and returns a string obtained
concatenating together the characters in the first string followed
by those in the second. See concatenate.