Reference: Green 1949

Green, MM. 1949. The classification of West African tone languages: Igbo and Efik. Africa 19(3). 213–219. Cambridge University Press.

@article{green1949classification,
  author    = {Green, MM},
  journal   = {Africa},
  number    = {3},
  pages     = {213–219},
  publisher = {Cambridge University Press},
  title     = {The classification of West African tone languages: Igbo and Efik},
  volume    = {19},
  year      = {1949}
}