 Admissible sequence of Steenrod squares

An index sequence obeying the displayed inequalities represents an admissible product ${\mathrm{Sq}}^{i_1}\cdots {\mathrm{Sq}}^{i_r}$. Its degree increment is the sum of the indices. The Adem relations rewrite every square monomial in terms of admissible ones, whose Steenrod excess controls universal instability.