48 years ago today, on February 25, 1977 (January 8, 1977), mathematicians Yang Le and Zhang Guanghou achieved important results in their research on function theory. Yang Le and Zhang Guanghou On February 25, 1977, Yang Le and Zhang Guanghou achieved important results in their research on function theory. For the first time in the world, an organic connection between the two main concepts in the study of function value distribution theory, "deficit value" and "singular direction", was found.