RIBBON 2-KNOTS WITH DISTINCT RIBBON TYPES
Abstract
A ribbon 2-knot is a 2-sphere in R4, which is obtained from m 2-spheres in R4 by connecting them with m - 1 pipes. Even in the case that a ribbon 2-knot K2 is constructed by two 2-spheres and one pipe, a way of constructing K2 is not always unique. That is, K2 might have presentations of two or more types.
The presentation that a pipe crosses two spheres n times is said to be an n-crossing ribbon presentation, and also n be the ribbon crossing number of this presentation.
In this note, we will show that for any positive integer i, there exists a ribbon 2-knot with presentations of two distinct types such that the difference of their ribbon crossing number is i; and in addition we will also show that for any positive integer j, there exists a ribbon 2-knot with presentations of j, distinct types such that they have the same ribbon crossing number.