Crystal base of the level 0 part of the modified quantum affine algebra $\tilde{U}_q (\widehat{{\frak s}{\frak l}_2})_0$ is given by path. Weyl group actions, extremal vectors and crystal structure of all irreducible components are described explicitly.

We study residues on a complete toric variety $X$, which are defined in terms of the homogeneous coordinate ring of $X$. We first prove a global transformation law for toric residues. When the fan of the toric variety has a simplicial cone of maximal dimension, we can produce an element with toric residue equal to 1. We also show that in certain situations, the toric residue is an isomorphism on an appropriate graded piece of the quotient ring. When $X$ is simplicial, we prove that the toric residue is a sum of local residues. In the case of equal degrees, we also show how to represent $X$ as a quotient $(Y\setminus\{0\})/C\ast$ such that the toric residue becomes the local residue at 0 in $Y$.

We present some basic identities for hypergeometric functions associated with the integrals of Euler type. We give a geometrical proof for formulae such as the identity between the single and double integrals expressing Appell's hypergeometric series $F_1 (a, b, b^{\prime} c; x, y)$.

This paper generalizes the definition of mixed perverse sheaves to schemes of finite type over a number field. Their basic properties, e.g., characterization of simple objects, are shown.