R4RS 6.5.5  (exp number)  ==>  number
            (log number)  ==>  number
            (sin number)  ==>  number
            (cos number)  ==>  number
            (tan number)  ==>  number
            (asin number)  ==>  number
            (acos number)  ==>  number
            (atan number)  ==>  number

These procedures compute the usual transcendental functions.
LOG computes the natural logarithm of NUMBER (not the base ten
logarithm). ASIN, ACOS, and ATAN compute arcsine (sin^-1),
arccosine (cos^-1), and arctangent (tan^-1), respectively.
