. . . "FIGS. 8A and 8B are a front view and a sectional side view, respectively, of a receptacle in accordance with one embodiment of the invention, FIG. 8C is a sectional side view in a case that the plug of the conventional example 4 has been inserted into the receptacle, and FIG. 8D is a sectional side view in a case that the plug shown in FIGS. 6A through 6C has been inserted into the receptacle;" . .