Gene Wolfe's gone over my head again...SF-Lovers

I have heard that with very careful reading, it is possible to deduce the real name of the character "Number Five" in Gene Wolfe's The Fifth Head of Cerberus. Either I'm too dense, or it's something French (I can't speak it), but I've read the book twice this week, (and three other times in the past seven years) and I always come up blank. OK, Mr. Wolfe, UNCLE! I've recognized about half a dozen hints and allusions, but that's as far as I can go. If there's someone out there who knows the answer, please contact me. Curt Wiederhoeft curtw at euler.jsc.nasa.gov