linguistic:translation
Special cases

It is possible to sum fewer than 2 numbers:

These degenerate cases are usually only used when the summation notation gives a degenerate result in a special case.For example, if n = m {\displaystyle n=m} in the definition above, then there is only one term in the sum; if n = m − 1 {\displaystyle n=m-1}, then there is none.