Projected and near-projected embeddings

P. M. Akhmetiev ; S. A. Melikhov

Zapiski Nauchnykh Seminarov POMI, Representation theory, dynamical systems, combinatorial methods. Part XXXI, Tome 498 (2020), pp. 75-104

Résumé

A stable smooth map $f N\to M$ is called $k$-realizable if its composition with the inclusion $M\subset M\times\mathbb{R}^k$ is $C^0$-approximable by smooth embeddings; and a $k$-prem if the same composition is $C^\infty$-approximable by smooth embeddings, or, equivalently, if $f$ lifts vertically to a smooth embedding $N\hookrightarrow M\times\mathbb{R}^k$. It is obvious that if $f$ is a $k$-prem, then it is $k$-realizable. We refute the so-called “prem conjecture” that the converse holds. Namely, for each $n=4k+3\ge 15$ there exists a stable smooth immersion $S^n\looparrowright\mathbb{R}^{2n-7}$ that is $3$-realizable but is not a $3$-prem. We also prove the converse in a wide range of cases. A $k$-realizable stable smooth fold map $N^n\to M^{2n-q}$ is a $k$-prem if $q\le n$ and $q\le 2k-3$; or if $q$ and $k=1$; or if $q\in\{2k-1, 2k-2\}$ and $k\in\{2,4,8\}$ and $n$ is sufficiently large.