In mathematical analysis, Littlewood's 4/3 inequality, named after John Edensor Littlewood, is an inequality that holds for every complex-valued bilinear form defined on c0, the Banach space of scalar sequences that converge to zero. Precisely, let B:c0 × c0 → ℂ or IR be a bilinear form. Then the following holds: where The exponent 4/3 is optimal, i.e., cannot be improved by a smaller exponent. It is also known that for real scalars the aforementioned constant is sharp.