Abstract
It is known that a 2-knot has the triple point number less than two if and only if it is of ribbon-type. We prove that there is no 2-knot of triple point number two or three. Hence the 2-twist-spun trefoil, which is known as a 2-knot of triple point number four, is one of the simplest non-ribbon 2-knots.
Citation
Shin Satoh. "No 2-knot has triple point number two or three." Osaka J. Math. 42 (3) 543 - 556, September 2005.
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