Unions script based on datasets circles

Question

Can someone tell me if I made this good? I am not so sure, especially about one thing explained by second diagram: does this green region means values of X AND Z, or rather X OR Z?

I made some corrects in code, but it seems that I am not using parentheses correctly. Don't know if this code is good

-- 1
/*
// Values stored in Y, that are parts of X and Z
"Y NOT IN (Y EXCEPT (UNION OF X AND Y))"
*/
SELECT Val FROM Y
EXCEPT
SELECT Val FROM X
EXCEPT
SELECT Val FROM Z

-- 2
/*
// Values stored in Y, that are parts of X and Z
"Y NOT IN (Y EXCEPT (UNION OF X AND Y))"
*/
SELECT VAL FROM Y
INTERSECT (
    SELECT Val FROM Y
    EXCEPT
    SELECT Val FROM X
    EXCEPT
    SELECT Val FROM Z
)

-- 3
/*
// Values stored in X and Z. that are not a part of Y
"(UNION OF X & Z) EXCEPT Y"
*/
SELECT VAL FROM X
UNION
SELECT VAL FROM Z 
EXCEPT
SELECT VAL FROM Y

-- 4
/*
// Every value of X, and same values from Y and Z
"(Y NOT IN (Y EXCEPT (UNION OF X AND Y))) UNION X"
*/

SELECT Val FROM X
UNION(
SELECT Val FROM Y
INTERSECT
SELECT Val FROM Z)

Answer 1

I agree with 1,3 and 4 but 2 should be:

SELECT VAL FROM Y
EXCEPT (
SELECT Val FROM Y
EXCEPT
SELECT Val FROM X
EXCEPT
SELECT Val FROM Z

or alternatively:

(SELECT Val FROM Y
INTERSECT
SELECT Val FROM X)

UNION

(SELECT Val FROM Y
INTERSECT
SELECT Val FROM X)