The four chess puzzles are taken from the excellent web site
Chess Puzzles by Grandmasters which contain actual positions from
over the board games played by Grandmastes.
Bacrot vs Pascal Stefanski, Belfort, 1992
Bacrot vs Lothar Vogt, Arosa, 1996
Fischer vs J Bennett, San Francisco, 1957
Fischer vs Luis Sanchez, Santiago, 1959