[過去ﾛｸﾞ] 現代数学の系譜 工学物理雑談 古典ガロア理論も読む49 (658ﾚｽ)
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238(1): 2018/01/07(日)18:24 ID:WplCTiTS(2/4) AAS
>>236
いっておくけど、系 1.8 の結果は
有理数の点で不連続, 無理数の点で一様連続となるf : R → R は存在しない
まで拡張出来る。
245(2): 現代数学の系譜 雑談 古典ガロア理論も読む ◆e.a0E5TtKE 2018/01/07(日)20:46 ID:2l42E8SE(23/29) AAS
>>238
おっちゃん、どうも、スレ主です。
>いっておくけど、系 1.8 の結果は
>有理数の点で不連続, 無理数の点で一様連続となるf : R → R は存在しない
>まで拡張出来る。
ああ、下記だな”g fails to satisfy・・even any specified pointwise modulus of continuity condition on a co-meager set.”＆
”Let E be the set of points at which f is continuous and where at least one of the four Dini derivates of f is infinite.
Then E is co-meager in R (i.e. the complement of a first category set).”
繰返すが、
”any specified pointwise modulus of continuity condition” ＆ ”at least one of the four Dini derivates of f is infinite”
だから（特に後者Dini微分）、どこかの無理数の点で一様連続も破綻するだろうな
（>>40より）外部ﾘﾝｸ[jspa]:mathforum.org
THEOREM: Let g be continuous and discontinuous on sets of points that are each dense in the reals.
Then g fails to have a derivative on a co-meager (residual) set of points.
In fact, g fails to satisfy a pointwise Lipschitz condition, a pointwise Holder condition, or even any specified pointwise modulus of continuity condition on a co-meager set.
(Each co-meager set has c points in every interval.)
（>>41より）
REMARK BY RENFRO:
The last theorem follows from the following stronger and more general result.
Let f:R --> R be such that the sets of points at which f is continuous and discontinuous are each dense in R.
Let E be the set of points at which f is continuous and where at least one of the four Dini derivates of f is infinite.
Then E is co-meager in R (i.e. the complement of a first category set).
This was proved in H. M. Sengupta and B. K. Lahiri, "A note on derivatives of a function",
Bulletin of the Calcutta Mathematical Society 49 (1957), 189-191 [MR 20 #5257; Zbl 85.04502]. See also my note in item [15] below.
(引用終り)
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