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There is a fn:sum, but no fn:product That does not seem intuitive. Both are the basic commutative arithmetic operations, there should either be both or neither. It is also very useful to calculate the factorial: product(1 to $something) From that you can define the binomial (which could also be useful in the math: module): declare function binomial($n, $k) { product(($k + 1) to $n) div product(1 to (n - k)) } and work with combinatorics and stuff
It's very easy to define it yourself: let $product := fold-left(?, 1, function($x, $y){$x * $y})
But so is fn:sum and that is there And utility functions seem to have become popular again, like fn:contains-token