Some Remarks on Analytic Foliations and Analytic Branched Coverings. Ulrich Hirsch — 1980 Mathematische Annalen
On Regular Homotopy of Branched Coverings of the Sphere. Ulrich Hirsch — 1977 Manuscripta mathematica
Bordismus verzweigter Überlagerungen von niedrigdimensionalen Sphären. Ulrich Hirsch — 1979 Manuscripta mathematica