Sufficient conditions are obtained for a function harmonic in the disk and continuous at a boundary point to have a level curve emanating from the boundary point into the disk. The one-sided ...

William M. Boothby, The Topology of the Level Curves of Harmonic Functions with Critical Points, American Journal of Mathematics, Vol. 73, No. 3 (Jul., 1951), pp. 512-538 ...

On each model in series 14 there are two sets of curves that act much like the lines on two-dimensional graph paper. One set of curves, called the level curves of the surface, lies on horizontal ...