input: Write a python function to check if one string is the reverse of another.
  assert is_reverse("hello", "olleh") == True
  assert is_reverse("python", "nohtyp") == True
  assert is_reverse("test", "tset") == True
  assert is_reverse("hello", "world") == False
  assert is_reverse("abc", "cba") == True
output: def is_reverse(s1, s2):
      return s1 == s2[::-1]