Triangular vanishing of Young-symmetrizer products ($t>u⟹h_t{h}_u=0$)

For standard tableaux of the same shape and $h_t=c_t{r}_t$, $t>u$ in column-reading order of standard Young tableaux implies $h_t{h}_u=0$. If there were no row-column collision, each column of $u$ would select one entry from each eligible row of $t$. Its sorted first column is componentwise at least the row minima of $t$; equality fixes those selected entries and permits induction after deleting the column. Thus no collision implies $u\ge t$. A collision gives $r_t{c}_u=0$.