.BG
.FN sum
.FN prod
.TL
Sums and Products
.CS
sum(...)
prod(...)
.AG ...
numeric or complex objects.
Missing values (`NA's) are allowed, but will cause the value returned
to be `NA'.
.RT
the sum (product) of all the elements of all the arguments.
If the total length of all the arguments is 0, `sum' returns `0'
and `prod' returns `1'.
.EX
mean(x) \(<- function(x) sum(x)/length(x)
.KW math
.WR
