Guthrie, Malcolm. 1971. "D.20 Lega-Kalanga Group: D.21 Bali (Souh-East Bua, Bango), D.22 Amba (Hamba), D.23 Komo, D.25 Lega (Rega), D.27 Bangubangu, D.28a West Holoholo (Guha, Kalanga), D.28b East Holoholo." In Comparative Bantu, v. 2: 42-43. Gregg International.