All assassins had a full-length mirror in their rooms, because it would be a terrible insult to anyone to kill them when you were badly dressed.
Terry Pratchett, Pyramids
- Summation (Wikipedia)
In mathematics, summation is the addition of a sequence of numbers, called addends or summands; the result is their sum or total. Beside numbers, other types of values can be summed as well: functions, vectors, matrices, polynomials and, in general, elements of any type of mathematical objects on which an operation denoted “+” is defined.