@misc{W4292078529,
  author = {Krassimir Atanassov and George Gargov},
  title = {Interval valued intuitionistic fuzzy sets},
  year = {1989},
  howpublished = {Fuzzy Sets and Systems},
  doi = {https://doi.org/10.1016/0165-0114(89)90205-4}
}