character — a character.

generalized-boolean — a generalized boolean.

These functions test the case of a given character.

upper-case-p returns true if character is an uppercase character; otherwise, returns false.

lower-case-p returns true if character is a lowercase character; otherwise, returns false.

both-case-p returns true if character is a character with case; otherwise, returns false.

(upper-case-p #\A) → true 
(upper-case-p #\a) → false 
(both-case-p #\a) → true 
(both-case-p #\5) → false 
(lower-case-p #\5) → false 
(upper-case-p #\5) → false 
;; This next example presupposes an implementation 
;; in which #\Bell is an implementation-defined character. 
(lower-case-p #\Bell) → false

Should signal an error of type type-error if character is not a character.

char-upcase, char-downcase, Section 13.1.4.3 (Characters With Case), Section 13.1.10 (Documentation of Implementation-Defined Scripts)