Uniqueness of ribbon-concordance minimal representative in each concordance class

Determine whether every smooth knot concordance class contains a unique knot that is minimal with respect to the ribbon concordance partial order.

Background

Ribbon concordance minimality interacts with the structure of the smooth concordance group. Gordon explicitly asked whether each smooth concordance class admits a unique representative that is minimal under ribbon concordance.

An affirmative answer, together with a related question, would imply a generalization of the Slice–Ribbon Conjecture, highlighting the importance of resolving this problem.