input: Write a function that returns a lambda function to calculate the sum of two variables. Use the lambda function to print the sum of the given input values.
  
  assert (lambda a, b: a + b)(3, 4) == 7
  assert (lambda a, b: a + b)(0, 0) == 0
  assert (lambda a, b: a + b)(-1, 1) == 0
  assert (lambda a, b: a + b)(10, -5) == 5
  assert (lambda a, b: a + b)(7, 7) == 14
output: lambda a, b: a + b