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These notes comprise (i) a descriptive account of the history of the subjec
t showing how physics and mathematics interwove to develop a mathematical c
oncept of quantum manifold relevant to elementary particle theory; (ii) a d
etailed technical description, from scratch, of the spectral action formali
sm and computation. (C) 2000 American Institute of Physics. [S0022-2488(00)
01806-5].