  For finite subsets A_1,...,A_n of a field, their sumset is given by
{a_1+...+a_n: a_1 in A_1,...,a_n in A_n}. In this paper we study various
restricted sumsets of A_1,...,A_n with restrictions of the following forms:
a_i-a_j not in S_{ij}, or alpha_ia_i not=alpha_ja_j, or a_i+b_i not=a_j+b_j
(mod m_{ij}). Furthermore, we gain an insight into relations among recent
results on this area obtained in quite different ways.
