This is extreme nitpicking but I'd recommend seeing it as a reliability of a product of constituents. A sum of constituents is more likely to be a situation wh

This is extreme nitpicking but I'd recommend seeing it as a reliability of a product of constituents. A sum of constituents is more likely to be a situation where you're fine if at least one of the options works (e.g. a cluster with redundancy). This will actually get you a semiring (easy to check), although whether that is really useful remains to be seen. It's nice to have anyway.