The expression ‘1 mod 3’ represents the modulus operation, which finds the remainder of the division of one number by another.
In this case, when you divide 1 by 3, you can think of it like this: 3 goes into 1 zero times, since 1 is less than 3. The multiplication of 0 (which is how many times 3 fits into 1) by 3 gives you 0. To find the remainder, you subtract this product from the original number:
1 – (0 × 3) = 1 – 0 = 1
So, the remainder is 1. Therefore, 1 mod 3 = 1.