A problem about Feynman integrals on Riemannian manifolds Torriani, Hugo H. — 1987 Proceedings of the Winter School "Geometry and Physics"
Faithful integral and modular representations of the Klein bottle group Hugo H. Torriani — 1987 Colloquium Mathematicae
Profinite completions of the fundamental group of the Klein bottle Hugo H. Torriani — 1985 Czechoslovak Mathematical Journal