Proof is the ninth in an annual series of publications that features the best young practicing architects as selected by the Architectural League of New York in their annual Young Architects competition. Competition entrants wereasked to use the theme "proof" to frame their portfolios and critically evaluate their work. This required creating projectsthat acknowledge architectural design as a unique process that begins with a speculation and gains traction through the subsequent testing, confirming, checking, and rechecking that occurs before and after designs encounter the real world. Eachof the winners--Aranda/Lasch, Jinhee Park, ludens, PARA, PRODUCTORA, and Uni Architecture--confronted this year's theme with work that is original, and inspiring.