All graphs are set reconstructible if all 2-connected graphs are set reconstructible.

A monaural signal to artificial stereo signals converting and processing circuit for headphones comprises, a circuit which converts a monaural signal into artificial stereo signals, a circuit which adds localizing information of imaginary sources to the artificial stereo signals thus obtained, and a circuit which adds imaginary indirect sounds to the artificial stereo signals added with the localizing information. Due to the addition of the indirect sounds, the sound expansion felt by a listener listening to a headphone expands to regions outside the listener's head.