So You Think, the leading older horse in Europe, will make his next start in the Oct. 2 Prix de l’Arc de Triomphe, trainer Aidan O’Brien confirmed Thursday. “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,” O’Brien said in a posting on the website of Coolmore, So You Think’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-up plan if the going in Paris turns too soft for O’Brien’s liking early next month.So You Think, a New Zealand-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’s Stakes at Ascot. Since joining O’Brien’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-mile Melbourne Cup. Other prominent horses pointing to the Arc are last year’s winner Workforce, Sarafina, and 3-year-olds Nathaniel, Reliable Man, and Meandre.