Towards a theory of type structure

7)(D) = B[w][71t]#D] and delta is a functor from Funct(C, C) into C. Even before defining the functors arrow and delta, it can be shown that B maps every type expression into a functor from C T into C, that w = w' implies B[w] = B[w'], and that B[WlI: 2](~) = B[Wl][ D I t I B[w2](D) ] B[WlI~2](7) = B[Wl][ ~ I t I B[w2](~) ]