Challenge 2: An Inline ; Disjunction Rule — Possible Solution
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drink.pl:

drink(mary, X) :- X = wine ; X = beer.

Query:

    ?- drink(mary, X).
    X = wine ;
    X = beer.

Explanation:
drink(mary, X)'s body is a single disjunction: X = wine ; X = beer.
Prolog tries the LEFT alternative of the ; first, succeeding by
unifying X with wine and reporting that as the first answer. Pressing
; asks for the next alternative, which backtracks into the
disjunction and tries the RIGHT side instead, unifying X with beer.
This is the exact same ; mechanism used for the top-level's own
"next answer" prompt -- here it's just written explicitly inside a
rule body rather than being triggered implicitly by multiple matching
clauses.

WHY THIS WORKS AS AN ANSWER
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This writes a genuine inline ; disjunction exactly as the chapter
introduces it, and retrieves both alternatives, confirming rule-body
; behaves identically to the top-level's own "next answer" mechanism.