Wittgenstein began studying mechanical engineering. During his research he became interested in the foundations of mathematics, particularly after reading Bertrand Russell's "Principles of Mathematics" and Gottlob Frege's "Grundgesetze". In 1911 Wittgenstein visited Frege and Russell and discussed philosophy with them at great length. He made a great impression on Russell and started to work on the foundations of logic and mathematical logic. Russell saw Wittgenstein as a successor who would carry on his work.