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SUMMARY:Josef Svoboda (Caltech)
DTSTART:20261024T160000Z
DTEND:20261024T170000Z
DTSTAMP:20261023T115435Z
UID:MAAGC2026/4
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/MAAGC2026/4/
 ">Brieskorn homology 3-spheres\, GL(2\,Z) and the Stern—Brocot tree</a>\
 nby Josef Svoboda (Caltech) as part of MAAGC 2026\n\nLecture held in Templ
 e 1169.\n\nAbstract\nThe d-invariant of a homology sphere $\\Sigma(p\,q\,r
 )$ is a non-negative integer. It obstructs the existence of smooth contrac
 tible 4-manifolds with the boundary $\\Sigma(p\,q\,r)$.  By a result of El
 kies\, d vanishes exactly when the corresponding resolution (or plumbing) 
 lattice is diagonalizable. We completely characterize Brieskorn spheres $S
 igma(2\,q\,r)$ with d=0\, using the combinatorics of Stern—Brocot tree a
 nd free submonoids of GL(2\,Z). Joint work with Shimal Harichurn\, Isabell
 a Khan and András Némethi.\n
LOCATION:https://researchseminars.org/talk/MAAGC2026/4/
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