View source for Apolar nets

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Two nets given in the same domain $G$ of a two-dimensional manifold, where at each point $x\in G$ the tangent directions of one net harmonically subdivide the tangent directions of the other. Thus, for instance, the [[Asymptotic net|asymptotic net]] on a surface in a Euclidean space is apolar with respect to the net of curvature lines (cf. [[Curvature lines, net of|Curvature lines, net of]]).