26.3; gaps, 26.3; metals vs. insulators, 26.4 Band theory of solids, **26.1**--26.6 Basis: orthonormal, 8.3; change of, 8.5; completeness, 8.4; continuous, 8.4; position, 8.4; momentum, 8.4 Beam splitter, 1.6, **7.3**, 24.6, 27.5 Bell inequality, **24.4**--24.6; CHSH form, 24.5; derivation, 24.4; ex