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`isalpha'--alphabetic character predicate

     #include <ctype.h>
     int isalpha(int C);
`isalpha' is a macro which classifies ASCII integer values by table
lookup.  It is a predicate returning non-zero when C represents an
alphabetic ASCII character, and 0 otherwise.  It is defined only when
`isascii'(C) is true or C is EOF.
   You can use a compiled subroutine instead of the macro definition by
undefining the macro using ``#undef isalpha''.
`isalpha' returns non-zero if C is a letter (`A'-`Z' or `a'-`z').
`isalpha' is ANSI C.
   No supporting OS subroutines are required.