Complex sentence: In knot theory, a figure-eight knot (also called Listing's knot) is the unique knot with a crossing number of four, the smallest possible except for the unknot and trefoil knot.
Split into simpler sentences: In knot theory, a figure-eight knot (also called Listing's knot) is the unique knot with a crossing number of four. This is the smallest possible crossing number except for the unknot and trefoil knot.