So You Think, the leading older horse in Europe, will make his next start in the Oct. 2 Prix de l&rsquo;Arc de Triomphe, trainer Aidan O&rsquo;Brien confirmed Thursday. &ldquo;So You Think is in great form and all being well with him, the plan is to run in the Arc, given reasonable ground conditions,&rdquo; O&rsquo;Brien said in a posting on the website of Coolmore, So You Think&rsquo;s owner. The Oct. 14 Champion Stakes over 1 1/4 miles at Newmarket also had been mentioned as a possible target for So You Think and could be used as a back&#45;up plan if the going in Paris turns too soft for O&rsquo;Brien&rsquo;s liking early next month.So You Think, a New Zealand&#45;bred who was imported to Ireland from Australia late last year, has won 4 of 5 starts in 2011, including Group 1 victories over Workforce and Snow Fairy. His lone 2011 defeat was a neck loss at the hands of Rewilding in the Prince of Wales&rsquo;s Stakes at Ascot. Since joining O&rsquo;Brien&rsquo;s operation, So You Think has yet to race at a distance as far as 1 1/2 miles, the Arc trip, and he has yet to win beyond 1 1/4 miles, though he did finish third last year in the two&#45;mile Melbourne Cup. Other prominent horses pointing to the Arc are last year&rsquo;s winner Workforce, Sarafina, and 3&#45;year&#45;olds Nathaniel, Reliable Man, and Meandre.