alphabetic check for Oracle SQL* Plus

Hi,
I'm having problems with trying to constrain my SQL create table statement. I need to restrict a name to only having alphabetic characters. I have found out that isalphabetic returns 1 if true and 0 if false.
I have broken my create table statement down to the very basics, so I can figure out the problem. At the moment it is:


create table person(
    name VARCHAR(20) NOT NULL
    check(isalphabetic(name) = 1),
    primary key(name)
);
 This will not compile however. When I tried it in Oracle SQL*Plus (8i) it returned "invalid relational operator".
I'm assuming that the 'isalphabetic' function is not supported in Oracle 8i. I also know that square brackets are not supported, which eliminates the use of [a-zA-Z] as a check option.
Do ou have any ideas how I could enforce this restriction?
Thanks!