Topological canal foliations

Abstract : Regular canal surfaces of R-3 or S-3 admit foliations by circles: the characteristic circles of the envelope. In order to build a foliation of S3 with leaves being canal surfaces, one has to relax the condition "canal" a little ("weak canal condition") in order to accept isolated umbilics. Here, we define a topological condition which generalizes this "weak canal" condition imposed on leaves, and classify the foliations of compact orientable 3-manifolds we can obtain this way.