Still from Gauss.
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If a ≡ b (mod m) and c ≡ d (mod m)
then a + c ≡ b + d (mod m) observe (a + c) - (b + d) = (a - b) + (c - d)
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| Subtraction Rule follows from the above. |
By repeated application of the addition rule it follows:
One can
add an arbitrary set of congruences for the same modulus.
Another application of the addition rule is simply adding a given congruence to itself k times. Thus we have:
A congruence may be multiplied by an arbitrary integer