If "R" is an integral domain, with field of fractions "K", then we can describe the ring Γ("U","O""X") more concretely as follows. We say that an element "f" in "K" is regular at a point "P" in "X" if it can be represented as a fraction "f" = "a"/"b" with "b" not in "P". Note that this agrees with the notion of a regular function in algebraic geometry. Using this definition, we can describe Γ("U","O""X") as precisely the set of elements of "K" which are regular at every point "P" in "U".