@article{IsardZwicky1970,
  author    = {{Stephen D. Isard and Harold M. Zwicky}},
  title     = {{Three open questions in the theory of one-symbol Smullyan systems}},
  journal   = {{SIGACT News}},
  year      = {{1970}},
  pages     = {{11-19}},
  issue     = {{7}},
}