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new principles of expression will be used.

Before going any further, I must show you how the third and fourth principles work when they are taken together.
For there are some quite puzzling forms.

But first of all I must make you acquainted with a few words that are convenient in talking about these expressions.

In the figure last drawn, "It shall lighten" is singly enclosed; that is, one line, and one only, completely encircles it.
"It shall thunder" is doubly enclosed, since two portions of the line, and only two completely encircle it.
Suppose I make this assertion