input: Write a function to check if an element exists within a given list of integers.
  
  def element_exists(elem, list_int):
    return elem in list_int
  
  assert element_exists(5, [1, 2, 3, 4, 5])==True
  assert element_exists(3, [10, 20, 30])==False
  assert element_exists('a', ['a', 'b', 'c'])==True
  assert element_exists(100, [])==False
output: def element_exists(elem, list_int):
    return elem in list_int