input: Write a function to generate all possible combinations of two elements from a given list.
  assert combinations([1, 2, 3, 4], 2) == [(1, 2), (1, 3), (1, 4), (2, 3), (2, 4), (3, 4)]
  assert combinations(['a', 'b', 'c'], 2) == [('a', 'b'), ('a', 'c'), ('b', 'c')]
  assert combinations([1], 2) == []
  assert combinations([], 2) == []
output: from itertools import combinations as itertools_combinations
  
  def combinations(lst, n):
      return list(itertools_combinations(lst, n))