From the mid 17th century, Joseon mathematics had a new beginning and developed along two directions, namely the traditional mathematics and one influenced by western mathematics. A great Joseon mathematician if not the greatest, Hong JeongHa was able to complete the Song-Yuan mathematics in his book GuIlJib based on his studies of merely Suanxue Qimeng, YangHui Suanfa and Suanfa Tongzong. Although Hong JeongHa did not deal with the systems of equations of higher degrees and general systems of linear congruences, he had the more advanced theories of right triangles and equations together with the number theory. The purpose of this paper is to show that Hong was able to realize the completion through his perfect understanding of mathematical structures.

The book ${\ll}$Ceyuan Haijing${\gg}$ studies inscribed and circumscribed circles in a right triangle and shows equations that give the diameters of the circles. We discuss the development of mathematical contents written by the scholar Yang Zhaoyun in Qing dynasty on the contents of ${\ll}$Ceyuan Haijing${\gg}$ in his book ${\ll}$Jiuyong Yandai${\gg}$. He derived equations to find the diameters of the circles based on algebraic knowledge known in the Qing dynasty. In this paper, we conclude that Yang's methods in devising the equations include the Gou-Gu Theorem, mathematical expressions derived from Gou-Gu ratio table, and the technique of interchanging triangles and events. We conclude that the Gou-Gu ratio table was a very important tool when Yang devised the equations in ${\ll}$Ceyuan Haijing${\gg}$.

The book Su Hak Ip Mun(數學入門, Introduction to Mathematics) is one part of 5 sections of the book Seung Aeh Ill Chan(升厓日簒), which is a hand written manuscript in Chinese characters and the author and the date of writing is unknown. The book Seung Aeh Ill Chan begins with the song of division table so called Guguiga(九歸歌). We first investigate and compare the writing pattern of this with other old Korean mathematical books. Next, we investigate typical expression and calculation methods of mathematical contents and terminologies used in Su Hak Ip Mun and also figure out oddities of writing pattern of mathematical expression and cultural circumference of several problems dealt in the book. From these analysis and investigation, we estimate the writing date of Su Hak Ip Mun later than the year 1723 on which Su Ri Jeong On(數理精蘊) was first published. And we presumably guess that Guguiga and Su Hak Ip Mun are made not for practical use or theoretical purpose but for text to teach students.

This paper aims to evaluate works of Frege and G$\ddot{o}$del, who play the trigger role in development of logic, by Knowledge Change Model. It identifies where their positions are in the model respectively. For this purpose I suggest types of knowledge change and their criteria for the evaluation. Knowledge change are classified into five types according to the degree of its change: improvement, weak glorious revolution, glorious revolution, strong glorious revolution, and total revolution. Criteria to evaluate the change are its contents, influence, pervasive effects, and so forth. The Knowledge Change Model consists of the types and the criteria. I argue that in the model Frege belongs to the total revolution and G$\ddot{o}$del to the weak glorious revolution. If we accept that the revolution in logic initiated by Frege was completed by G$\ddot{o}$del, it is a natural conclusion.

This interdisciplinary study explores G$\ddot{o}$del's hermeneutics of the relationship between relativity theory and idealistic philosophy in terms of time. For G$\ddot{o}$del, Einstein's contribution to the physical realization of idealistic philosophy would be remarkable. We start with a historical background around G$\ddot{o}$del's paper for Einstein(1949a). From the perspective of G$\ddot{o}$del's cosmology, the second part addresses the relative nature of time, and the next then investigates the rotating model of universes. G$\ddot{o}$del's own results show that the temporal conditions of relativity and idealistic philosophy are satisfiable in the mathematical model of rotating universes. Thus, it could be asserted to travel into any region of the past, present or future, and back again.

When imaginary numbers were first encountered in the 16th century, mathematicians were able to calculate the imaginary numbers the same as they are today. However, it required 200 years to mathematically acknowledge the existence of imaginary numbers. The new mathematical situation that arose with a development in mathematics required a harmony of real numbers and imaginary numbers. As a result, the concept of complex number became clear. A history behind the development of complex numbers involved a process of determining a comprehensive perspective that ties real numbers and imaginary numbers in a single category, complex numbers. This came after a resolution of conflict between real numbers and imaginary numbers. This study identified the new perspective and way of mathematical thinking emerging from resolving the conflicts. Also educational implications of the analysis were discussed.

The $L^1$-convergence of Fourier series problems through additional assumptions for Fourier coefficients were presented by W. H. Young in 1913. We say that they are the classical results. Using modified trigonometric series is the convenience method to study the $L^1$-convergence of Fourier series problems. they are called the neoclassical results. This study concerns with the $L^1$-convergence of Fourier series. We introduce the classical and neoclassical results of $L^1$-convergence sequentially. In particular, we investigate $L^1$-convergence results focused on the results of Bhatia's studies. In conclusion, we present the research minor lineage of Bhatia's studies and compare the classes of $L^1$-convergence mutually.