All uncountable cardinals can be singular

@hellishly_so https://t.co/TLGwkA3z80

I don't have a precise question to ask, but it's not even clear to me whether a b-countable union of b-countable sets is b-countable. Nor is it clear to me whether all sets are b-countable in a model where all uncountable cardinals are singular (see: http

@shota__math @chiba_tus_rscl ZFCを仮定すると任意の無限基数κについてκ^+は正則(つまりcf(κ^+)=κ^+)です。 一方ZF+任意の非加算基数が特異基数の無矛盾性がGitikによって証明されています。 https://t.co/akcahSf2TO

@SamucaMat @AsafKaragila @KamerynJW This was shown in a famous paper by Moti. MR0576462 (81h:03096) Gitik, M. All uncountable cardinals can be singular. Israel J. Math. 35 (1980), no. 1-2, 61–88. https://t.co/aHFO3CuIUY

@MatsuBasho Je connaissais pas le vocabulaire. Ms si je me réfère à l'abstract de ça http://t.co/BwyeNas0zN Effectivement, c impressionnant!