MathDB
Covering common points

Source: Miklós Schweitzer 2018 P10

November 18, 2018
college contests

Problem Statement

In 3-dimensional hyperbolic space, we are given a plane PP and four distinct straight lines: the lines a1a_1 and a2a_2 are perpendicular to PP; while the lines r1r_1 and r2r_2 do not intersect PP, and their distances from PP are equal. Denote by SiS_i the surface of revolution obtained by rotating rir_i around aia_i. Show that the common points of S1S_1 and S2S_2 can be covered by two planes.