Illmer, Martin MPI for Comparative and International Private Law, Max Planck Society;
https://max-eup2012.mpipriv.de/index.php/Contract_(Formation) (Any fulltext)
Illmer, M. (2012). Contract (Formation). In J. Basedow, K. J. Hopt, & R. Zimmermann (Eds.), The Max Planck Encyclopedia of European Private Law (pp. 378-383). Oxford: Oxford University Press.