--
-- util__logical_negation/1
--
create or replace function util__logical_negation(
  boolean
) returns bool as $$

declare
        true_or_false alias for $1;
begin
      IF true_or_false is null THEN
        return null;
      ELSE IF true_or_false = 'f' THEN
        return 't';   
      ELSE 
        return 'f';   
      END IF; END IF;
END;$$ language plpgsql;