On the boundary of fuzzy sets

@article{CuchilloIbez1997OnTB,
  title={On the boundary of fuzzy sets},
  author={Eduardo Cuchillo-Ib{\'a}{\~n}ez and Juan Tarr{\'e}s},
  journal={Fuzzy Sets and Systems},
  year={1997},
  volume={89},
  pages={113-119}
}