A graph is called a quasi-graph if the case of an edge of the graph equals its inverse is allowed. A graph of groups is called a quasi-graph of groups if the corresponding graph is a quasi-graph. An element g of a group G is called inverter if there exists a tree X, where G acts such that g transfers an edge of X into its inverse. In this paper, we show that if G is a fundamental group of a quasi-graph of groups and if H is a finite normal subgroup of G containing no inverter elements, then the quotient group  is a fundamental group of a quasi-graph of groups.

quasi-graphs of groups, groups acting on trees.