The C! is a way to reward a noder for submitting a particularly good writeup whether it be factual, humorous or artistic. Basically, a way of saying you appreciated the writeup and wanted to let the author know and give the writeup more attention than it would have had otherwise. C!ing someone's writeup earns it a place in the Cool Archive and the front page. E2 will also reward that user with 20 XP.

You get the power to C! writeups beginning at 4th level. A writeup can accrue any number of C!s but a user can C! any given writeup only once. Further C!s must be given by other users. For details on C!s and the rest of the level system see the voting/experience system document.

Cool Man Eddie will msg you in the Chatterbox every time somebody C!s one of your writeups, telling you who did it. If you don't want Eddie turned on you can uncheck a box in User settings. You can also enable a "cool safety" so you don't accidentally C! somebody's writeup.

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E2 Glossary

If you did all of your arithmetic in hexadecimal, then C! would equal

C * B * A * 9 * 8 * 7 * 6 * 5 * 4 * 3 * 2 * 1

Or 0x1C8CFC00

The decimal equivalents of C! and 0x1C8CFC00 are 12! and 479,001,600, respectively.

In certain mathematician circles, C! is also a shorthand term for "contradiction." The clearest example of its proper usage can be found in a problem involving solving a system of equations.

Suppose that you are given the following system to solve:

(i) x + 4y - z = 4
(ii) 3x - 2y + 5z = 6
(iii) 5x + 6y + 3z = 13

One solution1 to this system involves eliminating one of the variables and then adding or subtracting the resulting equations. Let us add (iii) with 3*(i).

3*(i) 3x + 12y - 3z = 12
(iii) 5x + 6y + 3z = 13
(iv) 8x + 18y = 25

We would then add 5*(i) to (ii) to garner a second equation without a "z" term.

5*(i) 5x + 20y - 5z = 20
(ii) 3x - 2y + 5z = 6
(v) 8x + 18y = 26

Subtracting (iv) from (v) produces the result 0=1 which immediately implies a contradiction. Namely C!. Therefore, a solution with only contradictory solutions C! has no solutions.

1Other solution methods include but are not limited to the iterative method, back substitution, matrices, and graphs.

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