Semi-parallel time-like surfaces in Lorentzian spacetime forms (Q1360120)

The notion `semi-parallel' refers to the integrability condition of the parallelity of the second fundamental form. The underlying connection here is \(\overline\nabla=\nabla+\nabla^\perp\). The surfaces in the title of the paper are classified as follows: they are either totally umbilical or they have a flat connection \(\overline\nabla\). The latter type is classified further in terms of second-order envelopes.