PittV88'

@article{DBLP:journals/jacm/PittV88,
  author    = {Leonard Pitt and
               Leslie G. Valiant},
  title     = {Computational limitations on learning from examples},
  journal   = {J. ACM},
  volume    = {35},
  number    = {4},
  year      = {1988},
  pages     = {965-984},
  ee        = {http://doi.acm.org/10.1145/48014.63140},
  bibsource = {DBLP, http://dblp.uni-trier.de}
}