The greek letters in the character codes are questionable. In the Hungarian translation (which is based on the older editions), the three greek letters are 10 Delta, 20 Sigma and 21 Pi. In the English dead-tree version of TAOCP vol 3 that zzo38 consulted, the letters are 10 Theta, 20 Phi, 21 Pi. In the PDF e-book versions of the original English TAOCP, although the text mentions greek letters, the actual greek letters are messed up, and three accent marks appear instead: 10 acute accent, 20 ring accent, 21 double acute accent. This is probably a font encoding mistake: in TeX fonts of the LaTeX 8t encoding, those accent signs are in positions 0x01, 0x06, 0x05 respectively, whereas those positions have the greek letters Delta, Sigma, Pi in vanilla computer modern cmtt fonts (the original TeX encoding).