input: Write a python function to calculate the probability of two independent events occurring simultaneously.
  assert probability_of_two_events(0.5, 0.5) == 0.25
  assert probability_of_two_events(0.1, 0.2) == 0.02
  assert probability_of_two_events(0.6, 0.7) == 0.42
output: def probability_of_two_events(p1, p2):
      return p1 * p2