Quantitative and qualitative estimates on the norm of products of polynomials

When for the first time, in 1987, a Banach space X and a bounded operator T : X → X without nontrivial invariant subspaces was constructed, one of the many tools used was a series of estimates on the norm of a product of polynomials. Here, we continue this study of estimates on the norm of a product of polynomials by, on the one hand, extending some results due to Beauzamy and Enflo and, on the other, observing that an inequality by Borwein and Erdelyi holds in a more general context.