Loose Pin

[garykevinware]

When Neville Stern first started solving, on Gary's Gems, he couldn't quite understand how a pinned piece could deliver checkmate. I was eventually able to explain it to his satisfaction. In reading Encyclopedia of Chess Problems: Themes and Terms by Milan Velimirovic and Kari Valtonen, I found out that there are a number of different types of composed chess problems in which that is the theme. "Loose Pin: A pin in which the pinned piece can move along the pin-line. This feature is thematically exploited in, for instance, Avner Mechanism, Bograd theme, Costachel theme, Cristoffanini theme, Leibovici Interference and Pelle theme." We'll look at a number of examples, over the next few weeks.
"Bograd Theme: The key piece unpins white thematic piece which threatens mate. Black re-pins it by a Pelle move, move by pinned piece, but also closes a black line, allowing the white thematic piece to mate also by a Pelle move, i.e. by moving along the pin-line."



Leib Bograd Wiener Schachzeitung 1937 #2

"Pelle Theme: All the moves in thematic variation(s) are made by pinned pieces."



Charles Pelle 10.cm Pat Ty 1938 #2

"Pelle Move: Move by pinned piece."



Isaak S. Birbrager Shakhmaty v SSSR 1950 #2



Giorgio Guidelli Good Companion 1915 #2

If you don't have a screw loose, you should be able to find the 'loose pins', and send me a complete variation to each problem, at garykevinware@yahoo.com , by next Wednesday, for 8 points.

[garykevinware]

Here are the solutions to last week's problems:
Bograd #2-
1 Kb6! ~ 2 Qd4#
1...Qe6 2 Qc6#
1...Ne2 2 Nf2#
1...Nf5 2 Bf3#
1...Bd5 2 Qf4#
Pelle #2-
1 Rg2! ~ 2 Qg7#
1...Qe5 2 Qf4#
1...Rg5 2 Qxg5#
1...e5 2 Qg6#
Birbrager #2-
1 Qa1 ~ 2 Qxd4#
1...Kd6 2 Rd7#
1...Kxb4 2 Rb7#
1...Bd5(xe4) 2 Rc7#
1...Be3 2 Rf7#
1...Rd3 2 Rg7#
"5 Pelle moves"
Guidelli #2-
1 Qd4! ~ 2 Qf6#
1...Qc5 2 Rxe4#
1...Qe5 2 Nxe4#
1...Qf5 2 Qg7#
1...Re6 2 2 Nxf7#
1...Bf5 2 Rxf5#
1...Rg8 2 Rxe4#