| procedure: - z1 z2
 | procedure: - z
 | procedure: - z1 z2 ...
 | procedure: / z1 z2
 | procedure: / z
 | procedure: / z1 z2 ...
 |
 |     With two or more arguments, these procedures return the difference
 |     or quotient of their arguments, associating to the left.  With one
 |     argument, however, they return the additive or multiplicative
 |     inverse of their argument.
 |
 | ...
 |
 | (/ 0.0)                                ==>  +nan.0
 | (/ 1.0 0)                              ==>  +inf.0
 | (/ -1 0.0)                             ==>  -inf.0
 | (/ +inf.0)                             ==>  0.0

If 0.0 is the multiplicative inverse of +inf.0, then +inf.0 must be
multiplicative inverse of 0.0.  But (/ 0.0) ==> +nan.0.  Which line is
correct?