1. Girard, J. Y.: 1981, ?? 2 1 -logic, part I: dilators?, Ann. Math. Log. 21, 75?219. (The basic text on dilators.)
2. Girard, J. Y.: ?Proof-theory and logical complexity?, to appear: at editions Bibliopolis, Napoli. (Chapters 8?12 of this book present the most systematic available description of ? 2 1 -logic.)
3. Girard, J. Y. and H. R. Jervell: ?? 2 1 -logic?, in preparation for editions North Holland. (This book will follow the viewpoint of trees: all kinds of dendroids ...)
4. Van de Wiele, J.: 1982, ?Recursive dilators and generalized recursions?, in Stern (ed.) Proc. Herbrand Symp., North Holland. (This paper gives an equivalence between two notions of generalized recursion, by means of dilators; these notions were not thought as equivalent before.)
5. Girard, J. Y. and D. Normann: ?Set-recursion and ? 2 1 -logic?, submitted for publication. (This paper gives an introduction to ? 2 1 -logic, viewed from the standpoint of recursion theory; it also gives a relativization of Van de Wiele's result, and as a corollary, we obtain section 8.2.)