I probably discovered America… but this is very LISP-like 
WITH T1 as ( SELECT SNO AS SA, CITY FROM S ) ,
T2 as ( SELECT SNO AS SB, CITY FROM S ) ,
T3 as ( SELECT * from T1 NATURAL JOIN T2 ) ,
T4 AS ( SELECT * FROM T3 WHERE SA < SB )
SELECT SA, SB FROM T4
This is what you get from reading CISP and ‘SQL and Relational theory‘ in a row.
PS
Dreamed about newbie installing Linux on himself and attracting zillions of nuclear cyber-cooties. The moral was : always use Windows!
