The story
Named after Johannes Trolle Petersen (later Johannes Hjelmslev) and Frank Morley.
Etymology from Wiktionary, CC BY-SA 4.0.
Petersen-Morley theorem
Today it means: A theorem stating 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. Full definition →