Quantum critical point and van Hove singularity in La$_{2-x-y}$Sr$_x$Nd$_y$CuO$_4$

By means of Zn substitution, thermopower and magnetic measurements we locate, distinguish and track the evolution of the pseudogap critical point and the van Hove singularity as a function of Nd content and relate these to pressure dependent effects in the Nd-free compound. The results have generic implications for all HTS cuprates.