On Uniqueness of End Sums and 1-handles at Infinity
For oriented manifolds of dimension at least 4 that are simply connected at infinity, it is known that end summing is a uniquely defined operation. Calcut and Haggerty showed that more complicated fundamental group behavior at infinity can lead to nonuniqueness. We examine how and when uniqueness fails. Examples are given, in the categories top, pl and diff, of nonuniqueness that cannot be detected in a weaker category (including the homotopy category). In contrast, uniqueness is proved for Mittag-Leffler ends, and generalized to allow slides and cancellation of (possibly infinite) collections of 0– and 1–handles at infinity. Various applications are presented, including an analysis of how the monoid of smooth manifolds homeomorphic to R4 acts on the smoothings of any noncompact 4–manifold.
Calcut, Jack S., and Robert E. Gompf. 2019. "On Uniqueness of End Sums and 1-handles at Infinity." Algebraic and Geometric Topology 19(3): 1299-1339.
Mathematical Sciences Publishers (MSP)
Algebraic & Geometric Topology
End sum, Connected sum at infinity, Mittag-Leffler, Semistable end, Exotic smoothing