New procedures:

. (log1p x) = log (1 + x) for any x in (-1, +\infty), -inf for -1.
  [The primitive flo:log1p has a range restriction due to the Intel
  i387 CPU instruction.]
. (expm1 x) = e^x - 1 for any real x.
  [The primitive flo:expm1 has a range restriction due to the Intel
  i387 CPU instruction.]
. (log1mexp x) = log (1 - e^x), for x < 0
. (log1pexp x) = log (1 + e^x)
. (logistic x) = 1/(1 + e^{-x}), inverse of logit
. (logit p) = log p/(1 - p), inverse of logistic
. (log-logistic x) = log 1/(1 + e^{-x}), inverse of logit-exp
. (logit-exp t) = log e^t/(1 - e^t), inverse of log-logistic
. (logit1/2+ p) = (logit (+ 1/2 p)), inverse of logistic-1/2
. (logistic-1/2 x) = (- (logistic x) 1/2), inverse of logit1/2+
. (logsumexp (list x y z ...)) = log (e^x + e^y + e^z + ...),
  guaranteed not to overflow or underflow
. (copysign m s) returns a real number with the magnitude of m and
  the sign of s.
