From Bruno Angelin:

Re: Physicists extract light from seeming emptiness (Nov. 18): In the article:

"That's be­cause the equi­val­ence of en­er­gy and mass, dis­cov­ered by Ein­stein."

The equivalence of energy and mass was discovered by Olinto de Pretto. Einstein proposed the theory of relativity, using the same equation and the same meaning that De Pretto has published two years before. Please do your homework there.