CHAR-DOWNCASE

turn upper-case characters into lower-case characters 
Major Section:  PROGRAMMING

(Char-downcase x) is equal to #a when x is #A, #b when x is #B, ..., and #z when x is #Z, and is x for any other character.

The guard for char-downcase requires its argument to be a standard character (see standard-char-p).

Char-downcase is a Common Lisp function. See any Common Lisp documentation for more information.