Here is the statement :
Let $A \in \mathcal{M}_n(\mathbb{C})$. Then for any submultiplicative matrix norm $N$ (induced or not) we have : $\rho(A) \le N(A)$, where $\rho$ is the spectral radius of $A$.
So from which well-known mathematicians this little result come from ? According to several references, it could be Browne or Hirsch but it is not clear...
Thanks in advance !