How to reference a subquery column alias?

Hello

Yesterday a list user solved me a problem with a sententence with two
subqueries. The solution was this:

SELECT remota_id,min(hora),max(hora), (SELECT caudal FROM historicos
WHERE remota_id=ooo.remota_id AND hora=min(ooo.hora)) as min_caudal,
(SELECT caudal FROM historicos WHERE remota_id=ooo.remota_id AND
hora=max(ooo.hora)) as max_caudal from historicos AS ooo GROUP BY
remota_id ORDER BY remota_id;

The issue now is i want to do some calculations with the subqueries
columns (min_caudal and max_caudal), for example adding them. (Get a new
column with max_caudal and min_caudal (alias) added)

I have tried to add in the SELECT;
,max_caudal+min_caudal as diferencia
,ooo.max_caudal+ooo.min_caudal as diferencia
,historicos.max_caudal+historicos.min_caudal as diferencia
,(SELECT max_caudal+min_caudal) as diferencia

I've read the SELECT and Table Expressions documentation pages, but
didn't found a solution.

Can anyone tell me how to reference or make the calculation with those
alias names?

TIA

Best,

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