"decode" the boolean value retruned from a stored function

I am trying to use the "decode" fuction to interpreat a returned bololean value from a store function to a char, but not much luck! Here is the example:

create or replace function PLUS_MINUS_BO (VAL1 in number, VAL2 in number) return boolean
is
begin
  retrun ((abs(val1 - val2)/val1) > .2); end PLUS_MINUS_BO;
/

Now, when I execute the following "select":

sql> select decode(PLUS_MINUS_BO(2,3), TRUE, '+', '-') from dual;

I get:

ERROR at line 1:
ORA-00904: invalide column name

Any hints?! Received on Wed Nov 13 1996 - 00:00:00 CET