* arith.c (rising_product): New static function.

(n_choose_k, n_perm_k): New functions.

* arith.h (n_choose_k, n_perm_k): Declared.

* eval.c (eval_init): New functions interned.

* txr.1: Documented.

1 files changed, 31 insertions, 0 deletions

diff --git a/txr.1 b/txr.1
index 20d871ef..a7812d15 100644
--- a/txr.1
+++ b/txr.1
@@ -8996,6 +8996,37 @@ The cum-norm-dist function calculates an approximation to the cumulative normal
 distribution function: the integral, of the normal distribution function, from
 negative infinity to the <argument>.
 
+.SS Functions n-choose-k and n-perm-k
+
+.TP
+Syntax:
+
+  (n-choose-k <n> <k>)
+  (n-perm-k <n> <k>)
+
+.TP
+Description:
+
+The n-choose-k function computes the binomial coefficient nCk which
+expresses the number of combinations of <k> items that can be chosen from
+a set of <n>, where combinations are subsets.
+
+The n-choose-k function computes nPk: the number of permutations of size <k>
+that can be drawn from a set of <n>, where permutations are sequences,
+whose order is significant.
+
+The calculations only make sense when <n> and <k> are nonnegative integers, and
+<k> does not exceed <n>. The behavior is not specified if these conditions
+are not met.
+
+.TP
+Description:
+
+The cum-norm-dist function calculates an approximation to the cumulative normal
+distribution function: the integral, of the normal distribution function, from
+negative infinity to the <argument>.
+
+
 .SS Functions fixnump, bignump, integerp, floatp, numberp
 
 .TP