Jugar piedra, papel y tijera

def jugarPiedraPapelTijera(a, b):
  if a == b:
    return "Empate"
  elif (a == "piedra" and b == "tijera") or (a == "papel" and b == "piedra") or (a == "tijera" and b == "papel"):
    return "Gana a"
  else:
    return "Gana b"

jugarPiedraPapelTijera("piedra", "tijera")