ORA-02429: cannot drop index used for enforcement of unique/primary key

create table tq84_p (
    id   integer,
    txt  varchar2(10),
    constraint tq84_p_pk primary key (id)
);
 
create table tq84_c (
    id_p   integer,
    val    number(5,2),
    constraint tq84_c_fk foreign key (id_p) references tq84_p
);
 
drop index tq84_p_pk;
-- ORA-02429: cannot drop index used for enforcement of unique/primary key
 
alter table tq84_p disable primary key cascade;
 
drop index tq84_p_pk;
-- ORA-01418: specified index does not exist
 
drop table tq84_c;
drop table tq84_p;