Show caption How can White, playing up the board, force checkmate in two moves, however Black defends? Leonard Barden on chess Chess: national solving championship opens to entries from Britain this week A prize fund of at least £1,225 is on offer, and success at Eton would lead to qualification for the 2019 world solving championship Leonard Barden Fri 8 Jun 2018 20.08 BST Share on Facebook

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This week’s puzzle marks the opening round of a national competition in which Guardian readers have traditionally performed strongly over many years.

You have to work out how White, playing as usual up the board in the diagram, can force checkmate in two moves, however Black defends.

The puzzle is the first stage of the Winton British Solving Championship, organised by the British Chess Problem Society and open to any British resident. Entry is free, and the prize fund will be at least £1,225.

If you would like to take part, simply send White’s first move to Nigel Dennis, Boundary House, 230 Greys Road, Henley-on-Thames, Oxon RG9 1QY or by email to winton@theproblemist.org.

Either way, include your name and home postcode, and mark your entry “Guardian”. If you will be under 18 on the closing date, 31 July, please also give your date of birth. After the closing date, all solvers will receive the answer and those who get it right will also be sent a postal round of eight problems, with plenty of time for solving.

The best 25-30 entries from the postal round plus the five best juniors will qualify for the final, to be staged on Saturday 23 February 2019 at Eton College. The winner there will qualify for the 2019 world solving championship.

As usual, the starter problem is tricky with a logjam of pieces in the bottom left-hand corner. There are several plausible near-misses and White’s first move is not obvious. Remember that routine checks and captures hardly ever work in composed problems. Good luck to all Guardian entrants.

Fabiano Caruana, the world No 2, took the €70,000 first prize at Stavanger on Thursday evening in dramatic fashion. At the start of the ninth and final round, world champion Magnus Carlsen shared the lead with the American trio of Caruana, Wesley So and Hikaru Nakamura on 4/7 with India’s ex-champion Vishy Anand half a point behind.

China’s world No4 Ding Liren withdrew with a broken hip from a cycle accident early in the tournament and his games were not counted.

The rules at Altibox Norway stated that a tie for first place would be decided by a speed play-off as the €70,000 had to be won outright.

Carlsen, who has never lost a tie-break play-off, drew very quickly, confident in his blitz skills, while Nakamura halved uneventfully and Anand defeated Russia’s Sergey Karjakin to join the leaders on 4.5/7.

In the Caruana v So game victory for either grandmaster would win the tournament outright. The position was complex, neither player wanted a draw, and both became short of time. Then disaster struck So, who failed to realise that he had reached the move 40 time control, played his 41st instantly, and blundered into defeat when a different move would have forced a draw and a five-way play-off.

Caruana’s comeback was complete from when he lost to Carlsen in the opening round. Besides winning first prize, the 25-year-old from St Louis cut his rival’s lead in the live ratings to just 19 points and, by winning on the Norwegian’s home turf, made a psychological point before their 12-game €1m world title match which starts in London on 9 November.