Petersen-Morley theorem (Wikipedia)

In geometry, the Petersen-Morley theorem states that, if a, b, c are three general skew lines in space, if a', b', c' are the lines of shortest distance respectively for the pairs (b,c), (c,a) and (a,b), and if p, q and r are the lines of shortest distance respectively for the pairs (a,a'), (b,b') and (c,c'), then there is a single line meeting at right angles all of p, q, and r.