Theorem 16.15. Suppose p is a prime number satisfying p ≡ 1 (mod 4).
1. The equation x² + y² = p has integer solutions, p factors nontrivially in ℤ[i], the polynomial x² + 1 factors nontrivially in ဴp[x], and -1 is a square in ဴp.
2. There are eight solutions to the equation x² + y² = p. Each solution (a, b) corresponds to a pair of irreducible Gaussian integers a + bi and a - bi such that p = (a + bi)(a - bi).
Exercise 16.12. Prove Theorem 16.15.