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 ###Isabelle/HOL
+* [Concrete Semantics - A Proof Assistant Approach by Tobias Nipkow and Gerwin Klein](http://www21.in.tum.de/~nipkow/Concrete-Semantics/) (PDF)
 * [Isabelle/HOL - A Proof Assistant for Higher-Order Logic by Tobias Nipkow and Lawrence C. Paulson and Markus Wenzel](http://isabelle.in.tum.de/doc/tutorial.pdf) (PDF)