- atanprocedure
These procedures are part of every implementation that supports general real numbers; they compute the usual transcendental functions. Real-ln computes the natural logarithm of x (not the base ten logarithm); real-log computes the logarithm of x base y, which is (/ (real-ln x) (real-ln y)) If arguments x and y are not both real; or if the correct result would not be real, then these procedures signal an error.