Maximum Principles for Minimal surfaces in R3 Having noncompact boundary and a uniqueness theorem for the helicoid. Friedrich Tomi; Jaime Ripoll — 1995 Manuscripta mathematica
Multi-helicoidal Euclidean submanifolds of constant sectional curvature. Ripoll, Jaime; Tojeiro, Ruy — 2001 Beiträge zur Algebra und Geometrie