local thread = require("thread")
print("Main program start")
local t1 = thread.create(function(a, b)
  print(a)
  os.sleep()
  print(b)
end, 'A', 'B')
local t2 = thread.create(function(c, d)
  print(c)
  os.sleep()
  os.sleep()
  print(d)
end, 'C', 'D')
thread.waitForAny({t1, t2})
print("Main program end")