class Emneside:
	def __init__(self):
		self._emner = []
		self._foreleser =  []
		self._studenter = []
		
	def leggtil_emne(self, emne):
		self._emner.append(emne)
		
	def leggtil_foreleser(self, foreleser, emne):
		if emne not in self._emner:
			print("Emnet finnes ikke")
			return
			
		self._foreleser.append(foreleser)
		emne.leggtil_foreleser(foreleser)
		foreleser.leggtil_emne(emne)
		
	def leggtil_student(self, student, emne):
		if emne not in self._emner:
			print("Emnet finnes ikke")
			return
			
		self._studenter.append(student)
		emne.leggtil_student(student)
		student.leggtil_emne(emne)
		
	def printtingsomprinterutalt(self):
		for emne in self._emner:
			print(emne)
			
		print("")
			
		for foreleser in self._foreleser:
			print(foreleser)
			
		print("")
			
		for student in self._studenter:
			print(student)