A crossing change exchanges the overpassing and underpassing strands at one crossing of a knot diagram. It generally changes the knot; unlike a Reidemeister move, it is not an isotopy. Two oriented band moves realize a crossing change as a genus-one knot cobordism.
An unknotting crossing is a crossing whose crossing change converts a knot into the unknot. It gives a genus-one knot cobordism to the unknot, and hence slice genus at most one after capping with a disk in .
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