  This is an introductory survey written in Japanese on classical integrability
from the viewpoint of symmetry reduction of 4-dimensional anti-self-dual
Yang-Mills equations. Twistor construction methods are discussed in detail in
4-dimension. Exact local solutions are, in this article, presented in terms of
quasideterminants in a compact form. Some integrable aspects in lower-dimension
are clarified in the context of the reduction. Noncommutative extension and
higher-dimensional extension are briefly discussed.
