• DOI https://doi.org/10.18177/sym.2020.60.sr.11480
  • PDF https://www.jstor.org/stable/26919803

  • DOI http://dx.doi.org/10.18177/sym.2012.52.sr.22
  • PDF https://www.jstor.org/stable/26564874

  • PDF https://www.jstor.org/stable/40374425

  • PDF https://www.jstor.org/stable/40374430
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