UNKNOTTING ORIENTABLE SURFACES IN THE 4-SPHERE
Jonathan A. Hillman, Akio Kawauchi · Journal of Knot Theory and Its Ramifications · 1995
We show that a topologically locally flat embedding of a closed orientable surface in the 4-sphere is isotopic to one whose image lies in the equatorial 3-sphere if and only if its exterior has an infinite cyclic fundamental group.