On the other hand we don't want to make them integral equations.
He was also the author of a book on integral equations.
Also integral equations can be studied in the complex domain.
They represent the differential forms of the integral equations given above.
In 1911, Lalescu wrote the first book ever on integral equations.
First, the boundary value problem is formulated as an integral equation.
He also wrote on algebraic geometry, number theory, and integral equations.
The first one is based upon the so-called complex Green's function and the reduction of the related boundary value problem to integral equations.
This point of view turned out to be particularly useful for the study of differential and integral equations.
The general theory of such integral equations is known as Fredholm theory.