A rational function is a ratio of two polynomials, where the denominator is not zero. It is defined for all real numbers except those that make the denominator zero, which are called the function's vertical asymptotes or points of discontinuity.
Divisor theory is a branch of algebraic geometry that deals with the study of divisors, which are formal sums of codimension-one subvarieties of an algebraic variety. It plays a crucial role in understanding the properties of varieties, particularly in the context of line bundles and the Riemann-Roch theorem.
Cartier divisors are a refinement of Weil divisors in algebraic geometry, providing a more flexible framework for handling divisors on varieties, particularly in the context of non-singular varieties. They are defined using local data and allow for the precise formulation of line bundles and their sections, playing a crucial role in the study of the Picard group and cohomology of varieties.