Dear Internet, please help me find a poorly-remembered book!
It was scifi, likely published in the 80s but conceivably late 70s or early 90s. I do not remember much of the plot but I remember that there was a playing card motif and I think also a harlequin motif.
The most distinctive feature I can remember is that there was a virtuoso pianist who would occasionally go into a fugue state; I believe he was one of the main characters.
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