"A density version of the Hales–Jewett theorem". Journal d'Analyse Mathématique. 57 (1): 64–119. doi:10.1007/BF03041066. MR 1191743. S2CID 123036744...

five was the Greek letter Π (pi), representing the Greek word for 'five' (pente). Numbers six through nine were written as a Π with vertical lines beside...