@article {MR0138088,
    AUTHOR = {Stone, A. H.},
     TITLE = {Absolute {$F\sb{\sigma }$} spaces},
   JOURNAL = {Proc. Amer. Math. Soc.},
  FJOURNAL = {Proceedings of the American Mathematical Society},
    VOLUME = {13},
      YEAR = {1962},
     PAGES = {495--499},
      ISSN = {0002-9939,1088-6826},
   MRCLASS = {54.99},
  MRNUMBER = {138088},
MRREVIEWER = {J.\ Segal},
       DOI = {10.2307/2034811},
       URL = {https://doi.org/10.2307/2034811},
}

@article {MR0219024,
    AUTHOR = {Liu, Chen-tung},
     TITLE = {Absolutely closed spaces},
   JOURNAL = {Trans. Amer. Math. Soc.},
  FJOURNAL = {Transactions of the American Mathematical Society},
    VOLUME = {130},
      YEAR = {1968},
     PAGES = {86--104},
      ISSN = {0002-9947,1088-6850},
   MRCLASS = {54.20},
  MRNUMBER = {219024},
MRREVIEWER = {R.\ F.\ Dickman, Jr.},
       DOI = {10.2307/1994772},
       URL = {https://doi.org/10.2307/1994772},
}



@article {MR0260958,
    AUTHOR = {Erd\H{o}s, P. and Stone, A. H.},
     TITLE = {On the sum of two {B}orel sets},
   JOURNAL = {Proc. Amer. Math. Soc.},
  FJOURNAL = {Proceedings of the American Mathematical Society},
    VOLUME = {25},
      YEAR = {1970},
     PAGES = {304--306},
      ISSN = {0002-9939,1088-6826},
   MRCLASS = {28.10 (54.00)},
  MRNUMBER = {260958},
MRREVIEWER = {E.\ R.\ Lorch},
       DOI = {10.2307/2037209},
       URL = {https://doi.org/10.2307/2037209},
}