  Certain significant fallacies are involved in discussions of the high-Tc
mechanism unsolved for over 30 years in cuprate superconductors. These
fallacies are explored with the aim of unravelling this mechanism. Moreover,
using polarised electronic Raman scattering in inhomogeneous underdoped cuprate
superconductors, the intrinsic nonlinear Raman spectrum is obtained by
subtracting the pseudogap characteristic of a nonlinear from the linear Raman
spectrum measured in the B2g mode of the node area below the critical
temperature. The intrinsic nonlinear behaviour implies the existence of the
nodal superconducting gap denying dx2-y2-wave pairing symmetry. An origin of
the nodal superconducting gap is discussed.
