ANSI Common Lisp 13 Characters 13.1 Character Concepts 13.1.4 Character Categories
188.8.131.52 Alphabetic CharactersThe alphabetic1 characters are a subset of the graphic characters. Of the standard characters, only these are the alphabetic1 characters:
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
a b c d e f g h i j k l m n o p q r s t u v w x y z
Any implementation-defined character that has case must be alphabetic1. For each implementation-defined graphic character that has no case, it is implementation-defined whether that character is alphabetic1.