Challenge 1: Unification in Both Argument Orders — Possible Solution
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SWI-Prolog session:

    ?- point(X, Y) = point(7, 9).
    X = 7,
    Y = 9.

    ?- point(7, 9) = point(X, Y).
    X = 7,
    Y = 9.

Explanation:
Both queries produce IDENTICAL bindings for X and Y, regardless of
which term is written on the left and which is on the right. This is
exactly the chapter's own central claim: unification has no concept
of "the pattern" and "the value" the way Haskell's pattern matching
does -- it's simply attempting to make two terms identical, and it
doesn't matter which side supplies the variables and which supplies
the concrete values. Swapping the order changes nothing about the
result.

WHY THIS WORKS AS AN ANSWER
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This directly demonstrates the chapter's own bidirectionality claim
by running the identical unification in both possible orders and
confirming the results are the same either way.