The ellipsis in mathematics as I understand it means and so forth.

http://en.wikipedia.org/wiki/Ellipsis

Half way down the page.

Normally dots should be used only where the pattern to be followed is clear, the exception being to show the indefinite continuation of an irrational number such as:

The last follows the definition given above.

]]>Also a statement that only addition is allowed would not be out of order.

I presumed, incorrectly that the dots in the drawing were to be replaced by symbols for mathematical operations. With the addition of parentheses it was not difficult to come up with a (useless) solution.

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