Kiyoshi Oka

Mathematician. Born in Wakayama Prefecture. Graduated from the Department of Mathematics, Faculty of Science, Kyoto Imperial University in 1925 (Taisho 14). Became an assistant professor at Kyoto University in 1929 (Showa 4) and studied in Paris for three years. During that time, he concluded that only superficial results had been achieved in the theory of multivariate complex functions, despite it being the most important topic in mathematics at the time, and decided to make this his own research topic before returning to Japan. After returning to Japan, he became an assistant professor at Hiroshima University of Literature and Science.

Between 1936 and 1942, Oka solved all of his immediate problems, including the "Cuzin problem," but the most important of them all was the "Lévy problem." If G is a regular domain, then G is locally convex in some sense. In other words, it is pseudoconvex. The inverse proposition of this is the Lévy problem, which asks, "If pseudoconvex, is it a regular domain?" and has been a difficult problem for many years. First, in the case of two variables, Oka solved it affirmatively, but in the case of general n dimensions, he introduced the concept of a local ideal and showed that it can also be solved affirmatively by the theory he established on top of it. This local ideal is the prototype of Henri Cartan's (1904-2008) concept of a sheaf, and the theory provides the connectivity of analytic sheafs. In this way, Oka can be said to have dug up a vein of the concept of a sheaf, which is useful in various fields of mathematics, by concretely immersing himself in multivariate analytic functions. In 1949 (Showa 24), he became a professor at Nara Women's University, received the Academy Prize in 1951, and was awarded the Order of Culture in 1960. They say that many geniuses are eccentric, and he was no stranger to such eccentricities. He also excelled in writing, and left behind many essays, including "Ten Stories of Spring Nights."

[Yasuo Akizuki]

"The Collected Works of Oka Kiyoshi, 5 volumes (1969, Gakken / 2008, Academic Press, Japan Library Center)" ▽ "Oka Kiyoshi: The Heart of Japan, by Oka Kiyoshi (1997, Japan Library Center)" ▽ "Oka Kiyoshi/Ko Lancheng: Oka Kiyoshi/Ko Lancheng, by Oka Kiyoshi and Ko Lancheng (Shingakusha Modern Romantic Library)" ▽ "Biography of Oka Kiyoshi: The Stars and Biography of Oka Kiyoshi: The Flowers, by Takase Masahito (2003, 2004, Kaimeisha)" ▽ "Song of the Heavens: The Life of Oka Kiyoshi, by Obikane Mitsutoshi (2003, Shinsensha)"

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

数学者。和歌山県生まれ。1925年（大正14）京都帝国大学理学部数学科卒業。1929年（昭和4）京大助教授となり、3年間パリに留学。その間、多変数複素関数論が当時数学において最重要な課題であるにもかかわらず、いまだ表皮的な成果しか得られていないと断じて、これを自己の研究課題と決意して帰国した。帰国後、広島文理科大学助教授となる。

　1936年から1942年の間に、当面の問題である「クザンの問題」などを、すべて解決したが、なかでも重要なのは「レビの問題」であった。Gが正則領域なら、Gは局所的にはある意味で凸である。すなわち擬凸である。これの逆の命題がレビの問題で「擬凸なら正則領域か」であり、年来の難問題であった。まず2変数の場合に、肯定的に解いたが、一般n次元のときには、局所イデアルの概念を導入し、そのうえにたてられた理論により、やはり肯定的に解けることを示したのである。この局所イデアルはアンリ・カルタンHenri Cartan（1904―2008）の層の概念の原型であり、その理論は解析的層の連接性を与えるものであった。このように岡は具体的に多変数解析関数に没入することによって、層という数学の各分野にわたって有効な概念の鉱脈を掘り当てたというべきである。1949年（昭和24）奈良女子大学教授に就任、1951年には学士院賞を受賞し、1960年には文化勲章を授与された。天才に奇行多しというが、彼にも奇行は少なくはなかった。また文才にも長じ、『春宵(しゅんしょう)十話』など多くの随筆を残した。

［秋月康夫］

『『岡潔集』全5巻（1969・学習研究社／2008・学術出版会、日本図書センター）』▽『岡潔著『岡潔　日本の心』（1997・日本図書センター）』▽『岡潔・胡蘭成著『岡潔／胡蘭成』（新学社近代浪漫派文庫）』▽『高瀬正仁著『評伝　岡潔――星の章』『評伝　岡潔――花の章』（2003、2004・海鳴社）』▽『帯金充利著『天上の歌――岡潔の生涯』（2003・新泉社）』

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