Consider the following code relationships:
‘Y & Z’ means ‘Y is the father of Z’.

‘Y # Z’ means ‘Y is the brother of Z’.

‘Y @ Z’ means ‘Y is the wife of Z’.

‘Y % Z’ means ‘Y is the sister of Z’.

How is Y related to T in the expression ‘S @ T  X % Y & Z’ (where indicates 'T is the son of X')?

Let's unpack the expression relation by relation:
S @ T⟹S is the wife of T (T is male).

T * X⟹T is the son of X.

X % Y⟹X is the sister of Y (X is female, making her the mother of T).

Y & Z⟹Y is the father of Z (Y is male).

Since X is the mother of T, and Y is the brother of X (X is the sister of Y), Y is the brother of T's mother.

Therefore, Y is the maternal uncle of T.