Solution
= Solution
For fixed hidden units, the supremum over $\|\alpha\|_1\le\lambda$ is $\lambda$ times the largest absolute unit correlation. Taking the further supremum over admissible $\beta_k$ gives exactly the displayed bound.
= Solution
For fixed hidden units, the supremum over $\|\alpha\|_1\le\lambda$ is $\lambda$ times the largest absolute unit correlation. Taking the further supremum over admissible $\beta_k$ gives exactly the displayed bound.