input: Write a function to suggest a valid Python syntax to calculate the sum of two variables using lambda. The function should return the lambda function.
  
  def suggest_sum_lambda():
      return lambda a, b: a + b
  
  # Test cases
  assert suggest_sum_lambda()(3, 4) == 7
  assert suggest_sum_lambda()(0, 0) == 0
  assert suggest_sum_lambda()(-1, 1) == 0
  assert suggest_sum_lambda()(10, -5) == 5
  
output: def suggest_sum_lambda():
      return lambda a, b: a + b