input: Write a python function to find all prime pairs that sum up to a given even number based on Goldbach's conjecture.
  assert Goldbach_conjecture(10) == [(7, 3), (5, 5)]
  assert Goldbach_conjecture(28) == [(23, 5), (19, 9), (17, 11)]
  assert Goldbach_conjecture(18) == [(13, 5), (11, 7)]
output: def Goldbach_conjecture(n):
      def is_prime(x):
          if x <= 1:
              return False
          if x <= 3:
              return True
          if x % 2 == 0 or x % 3 == 0:
              return False
          i = 5
          while i * i <= x:
              if x % i == 0 or x % (i + 2) == 0:
                  return False
              i += 6
          return True
      
      prime_pairs = []
      for i in range(2, n//2 + 1):
          if is_prime(i) and is_prime(n - i):
              prime_pairs.append((i, n - i))
      
      return prime_pairs