An aspect of the present invention simplifies maintenance of a software system by indicating the additional bug fixes that are to be tested when a bug is indicated to be fixed. The time between the generation of the signal and the return of the reflected signal provides an indication of the distance of the arc from the signal source. A viewline control unit determines positions and directions of the viewline while a storage unit stores computer graphics data including three-dimensional data of objects, walk-through attribute data and viewline data. A precursor comprising a precursor molecule is provided, with the precursor molecule being a polycyclic aromatic hydrocarbon and discotic molecule. This redistribution of weight causes the body to return to a horizontal position. The apparatus includes an eye gaze point detecting part analyzing a movement of a user’s pupils and detecting the user’s eye gaze point, and a beam irradiation part irradiating a beam at the user’s eye gaze point detected by the eye gaze point detecting part.