SQL: drop function restrict

Hello !!

I can't find a list for SQL alone, so I hope it is OK to post this question
here:

What have I misunderstood regarding:

*drop function a restrict;*


Why does the IBM i not complain in the following example that function a()
is in use of b() and can not be dropped.. I had the impression the it was
the idea of "restrict"

create function a () returns int
begin
return 1;
end;

create function b () returns int
begin
return a();
end;

drop function a restrict;