We prove that for any two quasi-Banach spaces
X and
Y and any
α>0 there exists a constant
37d49406349fbec548" title="Click to view the MathML source">γα>0 such that
holds for all linear and bounded operators
d25ba673f0454" title="Click to view the MathML source">T:X→Y. Here
ek(T) is the
k-th entropy number of
T and
ck(T) is the
k-th Gelfand number of
T. For Banach spaces
X and
Y this inequality is widely used and well-known as Carl's inequality. For general quasi-Banach spaces it is a new result.