In the Silly Post Correspondence Problem, the top string on each domino has the same length as the bottom string on that same domino. Show that SPCP is decidable.

N.png ... If gcd(a, m) = 1, then the unique solution xo to ax = b (mod m) is equal to (1) xo = ab (mod m) (2) xo = ab (mod m), where b is the inverse of b. (3) xo = ām (mod m), where ā is the inverse of a. (4) xo = āb (mod m), where ā is the inverse of a. A Choice (2) (B) Choice (1) Choice (4) (D) Choice (3)

For n 2 1, let a, be the number of ways to tile a 1 x n strip with 1 x 1 squares and 1 x 2 dominoes. The squares can be blue or red, while all dominoes are white. What is a2? Answer:

bottom set the low-order b bits of x to 1; the others to 0. For example, if b is 3, x should be 7. Pay special attention to the edge cases: if b is 32 x should be −1; if b is 0 x should be 0. Do not use in your solution. Provided input(s): b