“…We call a singular disk‐tangle for if - (1)each component of with unknotted boundary is a smooth, properly embedded, boundary parallel disk;
- (2)for each component of with knotted boundary , there is a 4‐ball such that is a 3‐ball containing and is a cone in and
- (3)the components of are disjoint when their boundaries are split and intersect transversely — away from all cone points — otherwise.
For example, if were the split union of a the torus link , whose components are three trefoils, and the Hopf link , then would consist of three cones on trefoils, which intersect pairwise transversely in six points, split union two smoothly embedded disks, which intersect transversely in a single point. Note that this is a generalization of the notion of a trivial disk‐tangle appearing elsewhere in the literature [6, 21, 24, 25]. Definition Let be a 4‐manifold equipped with a trisection , and let be a singular surface.…”