On surface braids of index four with at most two crossings
Tom 188 / 2005
Fundamenta Mathematicae 188 (2005), 167-193
MSC: Primary {57Q45}; Secondary {57Q35}.
DOI: 10.4064/fm188-0-9
Streszczenie
Let $\varGamma $ be a 4-chart with at most two crossings. We show that if the closure of the surface braid obtained from $\varGamma $ is one $2$-sphere, then the sphere is a ribbon surface.
