SQL> create table test (x int);

Table created.

SQL> begin
   2   for i in  1 .. 10  loop
   3   insert into test values(i);
   4   end loop;
   5   end;
   6   /

PL/SQL procedure successfully completed.

SQL> select * from test where not (x >  6  or x <  2 );

         X
 ----------
 
          2 
          3 
          4 
          5 
          6 

SQL> select * from test where (x <  6  or x >  2 );

         X
 ----------
 
          1 
          2 
          3 
          4 
          5 
          6 
          7 
          8 
          9 
         10 

SQL> select * from test where (x <=  6  and x >=  2 );

         X
 ----------
 
          2 
          3 
          4 
          5 
          6