Translated from the English description of how to solve the problem into SQL:
```
with cross
as (
select A, B
from (
select distinct A
from one
),
(
select distinct b
from two
)
)
select distinct a
from (
select *
from cross
except
select *
from two
)
;
```
Of course, "coding" the SQL is quite simple and proletarian once one has defined the problem solution (what programmers do).