SQL: Using restrict when dropping function and stored procedures

Hello.

What have I misunderstood regarding:

drop function xxxx *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 using the restrict keyword .. 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;

Same issue applies to procedures as well.