A (complex) Enriques surface is a projective smooth connected algebraic surface Y over C with H(Y,OY ) = H (Y,OY ) = (0), (Ω 2 Y ) ⊗ 2 ≃ OY but Ω 2 Y 6≃ OY ([CF]). In this note we give a short proof of the fact that the coarse moduli space of complex Enriques surfaces is quasi-affine. This was first shown by Borcherds [B] using the denominator function of a generalized Kac-Moody superalgebra (t...

For a quasidifferentiable function f defined on R 2 , it is proved, in the sense of Demyanov and Rubinov, that the following assertion [∂f (x),∂f (x)]∈Df (x) (∂f (x) + ∂f (x)), [∂f (x),∂f (x)]∈Df (x) (∂f (x) − ∂f (x)) ∈ Df (x) in this paper, where Df (x) denotes the set of all quasidifferentials of f at x. It is shown that this way can be viewed as an approach to determining or choosing a repre...