Mathematics is of fundamental importance for computer science. On the other hand, there are also many applications of computer science in mathematics, be it simulations, numerical calculations or computer algebra systems. Another interesting application of this kind is the implementation of logical methods for investigating mathematical proofs. In recent years, large electronic libraries of formalized proofs have been developed. Several case studies have demonstrated that, using such systems, it is possible to formalize proofs which are large enough to be of current research interest in mathematics. This situation creates a high potential for automating existing methods for the analysis of proofs, which have previously been applied only manually. This book is an investigation of such a method, and in particular of the results it provides about the mathematical content and structure of formal proofs.