The problem is not to hard to solve since Black is in stalemate. White must give black a move so how should it be done? A move of the wRh2 north will give the bK a flight (and sacrifice wS) but White must provide for this flight. The only way to do so is to go all the way up the file giving the wQ access to h7. Typical Sam Loyd key:
1.Rh8! Kxc2 2.Qh7
Here is the classic Bristol clearance problem and the reason for the namesake. A key that would baffle anyone and an unbelievable idea for the date: 1.Rh1!
The main line happens when the bBb5 moves to d7 or e8 in which case a flight for the bK is opened. The wQ can move to b1 making the threat Qb4 (notice the wQ keeps control of b6). However, the bB can move back to b5 defeating the threat because it blocks the wQ's guard on b6. And now we see the motivation for the key move.
1...Bd7 2.Qb1 Bb5 3.Qg1
A couple things to notice: the wBa1 is just a plug, it can be removed but then there would be two keys 1.Rh1 and Ra1. Second, I cannot find a purpose for the wRf3. This was probably put on the board to confuse solvers at the time.
Another classic and personal favorite! The above two problems have pure Bristol clearances because the clearing piece has no role other than to get out of the way. This time the clearance is not pure, but the effect is still astonishing. Here the wBe5 has to clear for two pieces: the wQ and the wR on a5 to make way for the threat. The reason the wB must stay on the diagonal is to respond to the check 1...BxQ+. It must go all the way to the corner square so the wQ can access g7. Moreover the unpinning effects are striking. Wonderful stuff!
1...c5 2.Qg7 (the reason for the clearance)
Here is a nice example of a Bristol clearance in which the wR clears for a wP. The Albino theme is also present:
Here is my Bristol offering. The problem is my first to appear in the prestigious British Chess Magazine. I use a twinning to achieve two maximum length Bristol clearances first with a wB and then with a wR with changes. Amazingly White has all of that wood but can't mount a threat in either part. This is one of those problems that you compose that stays near to your heart.
Notice that the wQ and wRs mate on the same squares b2 and h2 in the different parts. Moreover, an interesting aspect is the role of wBg7: it plays no active part in b) other than to stop cooks and it actually plays no active part in a) post key other than to make the key. My only lament is that I could not work in three variations in part b).
A modern try problem. Here there are two Bristol clearances with a king's battery and brilliant changes. The wK is bottled up and needs a place to go. Should the wR or wB be the ones to make the move?
Often it is the weaker pieces that are clearing the way for the stronger piece. In this example the opposite effect happens: the wQ clears the way for the wB and wR.
The question I asked myself when solving is why can't the wQ mate after all of the thematic defenses of the bR and bB on g3? It's because she controls the square d3. The icing on the cake is the changed mate after c6. A beautiful problem that won first prize in StrateGems. Poetry on the chess board.
How about Bristol clearances in a helpmate?
1.Qe4 Rh1 2.Bf5 Qg1
1.Rf2 c4 2.R8f5 Rc4
Excellently matched solutions in which the clearance happens so the rear piece can interfere on the clearance line of the other solution. Notice also we have a wP clearance.
This time we see two wR making the clearances with three outstanding changes between try and key.
Moreover, the key is both Bristol and anti-Bristol because it restricts the wPf2 from reaching f4.
Here we have an attractive position with no white pawns and the mirrored bK. It also shows two masked Bristol clearances: the bSs stand on the clearing line.
Wonderful harmony with the wQ and wB mating on e4 in the try play and the wQ and wR mating on d1 after the key.
Here is a nice little example of Bristol clearances combined with the Novotny theme.
Here is a neat 3 move idea: if the wRf2 or wSg2 were removed then the wQ can mate on b2. However, the bB can block the path. So why not let the bB annihilate these pieces.
1...Bxg2 2.Ra2 B~ 3.Qb2
1...Bxf2 2.Sh4 B~ 3.Qb2
A beautifully executed clearance of a wQ for a wB. The wQ must travel along the diagonal c3-g8 and surprisingly withdraw all the way out to g8. What a key that also abandons the set response to the promotion check on b1!
1.Qg8! >2.Bf7+ Kb1 3.Bxg6
We end with a recent 1st prize winner in the The Problemist. This wonderful problem has a pair of Bristol clearances with a partial switchback and white halfpin. To top it off there is a flight giving key. Just overall excellence.
1...c5,c6 2.Bf5 (Rd4?)
1...c6 2.Rd4 (Bf5?)
Interestingly the original version had 3 bRs. The separation of 1...c5,c6 and the matched play in both phases make this problem a true work of art.