Джерела

1)http://ito.vspu.net/index2.html
2)https://uk.wikipedia.org/wiki/%D0%93%D0%BE%D0%BB%D0%BE%D0%B2%D0%BD%D0%B0_%D1%81%D1%82%D0%BE%D1%80%D1%96%D0%BD%D0%BA%D0%B0
3)http://proridne.com/content/%D0%BF%D1%96%D1%81%D0%BD%D1%96/%D1%80%D0%BE%D0%BC%D0%B0%D0%BD%D1%81%D0%B8/