Challenge 3: Why Reusing X Across Clauses Doesn't Connect Them — Possible Solution
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// Each CLAUSE (each individual fact or rule) in Prolog gets its own,
// completely fresh, independent set of variables the moment it's
// used -- variable scope in Prolog is per-clause, not per-predicate
// and not per-file. Writing X in one clause and X again in a
// different clause of the SAME predicate looks, visually, like it
// might be "the same X" -- but the two X's are never actually the
// same variable at all. They just happen to share a spelling. This
// is genuinely different from ordinary lexical scoping in an
// imperative or functional language, where reusing a name in a
// nearby scope usually either shadows the outer one deliberately or
// produces a real "already defined" error -- Prolog does neither; it
// silently treats them as two unrelated variables with no warning.
//
// If a programmer genuinely needs two goals within the SAME clause
// to be related -- e.g. requiring that a value produced by one goal
// is used again by a second goal -- the correct approach is to use
// the SAME variable name within that ONE clause's own body, where
// Prolog's per-clause scoping actually does apply and does connect
// them. For example, in:
//
//     sibling(X, Y) :- parent(P, X), parent(P, Y), X \= Y.
//
// P genuinely IS shared correctly here, because all three goals --
// parent(P, X), parent(P, Y), and X \= Y -- belong to the SAME
// clause's body. It's only reuse ACROSS separate clauses (separate
// facts or separate rule definitions) that fails to connect anything,
// not reuse within one clause's own body.

WHY THIS WORKS AS AN ANSWER
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This correctly explains that Prolog's variable scoping is per-clause,
not per-predicate, and clarifies the real distinction the chapter's
warn-box is pointing at: reuse WITHIN one clause's body genuinely
connects variables, while reuse ACROSS separate clauses does not,
giving a concrete working example of the correct within-clause
pattern.