He's doing pure mathematics in his mind.

他在自己的脑海里思考纯粹的数学。

Nobody can ever say that Einstein is not a fantastic mathematician because at that moment the problem is distilled into pure mathematics.

没有人说爱因斯坦不是一位神奇的数学家,因为在那一刻问题被净化成纯粹的数学。