= Solution
Take the untwisted <Whitehead double> of a <trefoil knot>. The Whitehead pattern has <winding number of a satellite pattern> zero and becomes the <unknot> when its companion is the unknot. The <Satellite formula for the Alexander polynomial> therefore gives
$$
\Delta_{K_4}(t)\doteq\Delta_{P(U)}(t)\Delta_{T_{2,3}}(1)=1.
$$
The Whitehead pattern is geometrically essential in its solid torus, so the <satellite knot> with nontrivial companion $T_{2,3}$ is nontrivial. Hence $K_4$ is not isotopic to the unknot despite having trivial <Alexander polynomial of a knot>.
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