Or we might represent them as follows, according to the numerical order of the operations:—
The brackets, it should be understood, point out the relation in which the operations may be grouped, while the comma marks succession. The symbol + might be used for this latter purpose, but this would be liable to produce confusion, as + is also necessarily used to represent one class of the actual operations which are the subject of that succession. In accordance with this meaning attached to the comma, care must be taken when any one group of operations recurs more than once, as is represented above by
(11 ... 15), not to insert a comma after the number or letter prefixed to that group.
,(11 ... 15) would stand for an operation
followed by the group of operations (11 ... 15); instead of denoting the number of groups which are to follow each other.