Original sentence: However, as noted above, it has long been known that Maxwell's equations cannot claim fundamental validity (and indeed have been replaced by quantum electrodynamics), so Einstein preferred, in his foundational paper of 1905, to base special relativity on just the single feature of those equations (invariance of lightspeed) that is sufficient, together with the relativity principle, to derive special relativity.In some subsequent papers, whose purpose was to show that energy, in the form of electromagnetic radiation, conveys inertia (mass) from the emitting to the absorbing body, Einstein found it necessary to postulate not just invariant lightspeed but the entirety of Maxwell's equations.It is sometimes suggested that Maxwell's equations in their entirety could be adopted as the second postulate, rather than just postulating the one salient feature of Maxwell's equations (namely the invariance of light speed) that is sufficient to derive special relativity.Of course, this use of Maxwell's equations (relativistically interpreted) as a heuristic guide for inferring the equivalence of mass and energy should not be confused with a rejection or even a replacement of the lightspeed invariance postulate, because, as Einstein noted in his 1905 paper on the inertia of energy, the latter is contained in the former.This is not surprising, because the complete equivalence and transmutability of mass and energy does not follow strictly from the postulates of special relativity; additional postulates involving the behavior of actual forms of matter and energy are always required.. In his survey paper summarizing the status of special relativity in 1907 Einstein acknowledged that the reliance on Maxwell's equations (which he already knew to be invalid) was a deficiency in these arguments, but he justified it by saying that at least some features of Maxwell's equations were likely to survive in any revised theory of electrodynamics, so one could hope that results derived on the basis of Maxwell's equations would be at least heuristically useful
Edited sentence: Some people (including Einstein at times) believe that the second postulate is redundant because it follows from the first postulate applied to Maxwell's equations; other people disagree