1. What is the definition of the duality group $E_{7(7)}$ that appears in [${\cal N}=8$ Supergravity](http://en.wikipedia.org/wiki/N%3D8_Supergravity) and what are the basics properties? 

2. Moreover what is the relation with the Lie Algebra $E_7$? 

3. Please, provide some reference in your answer.