Obviously, this article is based on the corresponding section in the book of Yu. A. Kuznetsov. It is a bit unfortunate that it contains no pictures, though it is hard to say what should be pictured! I have two minor comments: -In the section on the "Multidimensional case": is the restriction three-dimensional? I would think "four-dimensional". -In the references, paper of Broer and Vegter: "codimansions" should be "codimensions"
THANKS, THE MISPRINTS ARE CORRECTED. YURI.
One trivial comment: there is a misprint in the word "transversally"