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 expression as a string.
  assert suggest_lambda_sum() == "(lambda a, b : a + b)"
  assert suggest_lambda_sum() == "(lambda a, b : a + b)"
  assert suggest_lambda_sum() == "(lambda a, b : a + b)"
  assert suggest_lambda_sum() == "(lambda a, b : a + b)"
  assert suggest_lambda_sum() == "(lambda a, b : a + b)"
output: def suggest_lambda_sum():
      return "(lambda a, b : a + b)"