R4RS 6.5.5  (exact->inexact number)  ==>  number
            (inexact->exact number)  ==>  number

EXACT->INEXACT returns an inexact representation of NUMBER. The
value returned is the inexact number that is numerically closest
to the argument.

INEXACT->EXACT returns an exact representation of NUMBER. The
value returned is the exact number that is numerically closest
to the argument.
