Function pellSatisfies

test/compute-engine/diophantine.test.ts:362–364

(D: bigint, N: bigint, x: bigint, y: bigint)

//

function pellSatisfies(D: bigint, N: bigint, x: bigint, y: bigint): boolean {
  return x * x - D * y * y === N;
}

/** `(x1,y1)·(x2,y2)` in `ℤ[√D]`. */
function pellMul(