How to reuse calculated columns avoiding duplicating the sql statement?

Question

I have a lots of calculated columns and they keep repeting themselves, one inside of the others, including nested cases statements.

There is a really simplified ver

Answer 1

Another option if someone is still interested:

with aa(a) as ( select 1+2 ) 
, bb(b) as ( select a+3 from aa ) 
,cc(c) as ( select b*7 from bb) 
SELECT aa.a, bb.b, cc.c 
from aa,bb,cc