Difficult - Problem: A mate in 6 chess problem delightful in its purity. Composed in 1910 by Nissl.
Correction: Composed by Thomas Davidson (horizontal mirror) in Montreal Daily Witness, 1899.
Difficult - Study: A very beautiful 1924 chess study by Troitsky. In this short video, Chess Queen Alexandra Kosteniuk shows you how to solve it to the end, you will enjoy it for sure.