In jazz, the strength of any ensemble comes from the linkages formed within the rhythm section, and the heart of every rhythm section lies in the interplay between bassist and drummer. This may be an elementary lesson in jazz anatomy, but it helps explain why this pickup band should sound healthier than most. Bassist John Webber and drummer George Fludas have worked together in New York; they know each other's moves, and that fact overrides even their individual excellence. Their solid but imaginative rhythmic springboard is the kind that allows a good pianist to flex his muscles, which means that Jodie Christian--a spectacular pianist--can indulge his own rhythmic virtuosity while reinvestigating familiar harmonies. In front will be young Eric Alexander on tenor; at anchor is Webber, who brings an old master's touch to the bass--dark walnut sound, impeccable time. Tonight, Bop Shop, 1807 W. Division; 235-3232.