Biquadratic Reciprocity Theorem
Gauss stated the reciprocity theorem for the case n = 4 x^4 congruent q (mod p) can be solved using the Gaussian integers as (π/σ)_4 (σ/π)_4 = (-1)^([(N(π) - 1)/4][(N(σ) - 1)/4]). Here, π and σ are distinct Gaussian primes, and N(a + b i) = a^2 + b^2 is the norm.