Love is not love, wrote Shakespeare, which alters when it alteration finds. In his selection of records this week, Jeremy Siep mann discovers the theme of love unaltered in music as diverse as a cantata by Schiitz, a Haydn opera. Weber's Invitation to the Dance (played by Artur Schna bel), and a folk song by Brahms. Atso to be heard are Wagner's Siegfried Idyll, and contributions in rather lighter vein from. among others. Bessie Smith and Vincent Youmans.