Update THANKS

THANKS

@@ -9,6 +9,9 @@
 3) https://webpen.com.ua/pages/linguistic_norm/emphasis.html
 4) https://studfiles.net/preview/3283593/
 5) https://uk.wikipedia.org/wiki/%D0%9E%D1%80%D1%84%D0%BE%D0%B5%D0%BF%D1%96%D1%8F_%D1%83%D0%BA%D1%80%D0%B0%D1%97%D0%BD%D1%81%D1%8C%D0%BA%D0%BE%D1%97_%D0%BC%D0%BE%D0%B2%D0%B8
+6) Graham Hutton. A tutorial on the universality and expressiveness of fold. J. Functional Programming 9 (4): 355–372, July 1999. Cambridge University Press
+Online access: http://www.cs.nott.ac.uk/~pszgmh/fold.pdf
+Last visited: 14/07/2019.
 
 English Translation
 
@@ -23,3 +26,6 @@ So, there were used such literal sources:
 3) https://webpen.com.ua/pages/linguistic_norm/emphasis.html
 4) https://studfiles.net/preview/3283593/
 5) https://uk.wikipedia.org/wiki/%D0%9E%D1%80%D1%84%D0%BE%D0%B5%D0%BF%D1%96%D1%8F_%D1%83%D0%BA%D1%80%D0%B0%D1%97%D0%BD%D1%81%D1%8C%D0%BA%D0%BE%D1%97_%D0%BC%D0%BE%D0%B2%D0%B8
+6) Graham Hutton. A tutorial on the universality and expressiveness of fold. J. Functional Programming 9 (4): 355–372, July 1999. Cambridge University Press
+Online access: http://www.cs.nott.ac.uk/~pszgmh/fold.pdf
+Last visited: 14/07/2019.