Notes
I had also a very friendly relationship with Steenrod, but this had naturally and gradually grown starting with his course in Mexico.
This section includes several technicalities, but readers not familiar with Topology need not stop reading, just consider them as labels (complex, real, (A), (a)...) that can be of some help in following in the story.
I found the first example of such a connected sum in the work of Dennis McGavran [35] on torus actions, after a long search in Mathematical Reviews, Google not being available at the time. This was a big surprise and an extremely valuable heuristic guide for our work. On the other hand, only one of McGavran’s examples was relevant for my problem. Furthermore, all his arguments are valid only in the PL-category and I have not been able to reconstruct his proofs in the smooth case, so the proof of my results had to be totally different from his. In the real case (see below) one obtains easily the surface of genus 5, so the fact that such connected sums appear in this question becomes less surprising.
This is a simple illustration of the fact that many topological properties of \(M_{1}\) and its generalizations are related to convexity properties of the coefficients.
This time it was Pepe who invited me, but clearly that was the result of a plot that included Alberto and Xavier Gómez Mont.
Up to now we do not know explicit diffeomorphisms between our varieties and the connected sums, only their existence by the h-cobordism theorem.
This took place during a conference for my 65th birthday, organized essentially by Pepe. Actually, Pepe organized everything from abroad through the web and did not even come to the conference, the local organizer was my former student León Kushner.
Actually, Laurent had told me that a referee suggested to them to include in the published version of [12] a connection with another work on the same objects, but this never attracted my attention. In the same way, had I accepted a conference for my 60th anniversary, Sam’s talk would have been different and maybe none of this would have happened.
Recall the beginning of this section.
Some readers must know what this meant: after three or four hours where Sam had spoken about several different questions (including ideas that he had long ago or had just occurred to him that day during breakfast) one is totally exhausted, while he is ready to go on for several more hours.
This lattice is equivalent to the lattice of points in \(\mathbf {R}^m\) with integral non-negative coordinates, where m is the number of facets of the polytope P corresponding to Z. In terms of polytopes this is given by the map \(J\mapsto P(J)\) (see [6], Theorem 2.4).
These examples are still quite geometric and simple. It should be said that the topologically more complicated examples, in particular those with non-trivial Massey products, are also numerous. See [18].
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In memory of Sam Gitler.
Partially supported by Project PAPIIT-DGAPA IN111415.
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López de Medrano, S. Samuel Gitler and the topology of intersections of quadrics. Bol. Soc. Mat. Mex. 23, 5–21 (2017). https://doi.org/10.1007/s40590-016-0148-0
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DOI: https://doi.org/10.1007/s40590-016-0148-0