 This, apparently, removed the incentive among the researchers for further investigations along these lines.However, the interest in this problem waxed again in the 1960s after Penrose published his theorems that linked the existence of a singularity of unknown character with some very general assumptions that did not have anything in common with a choice of reference frame.Other similar theorems were found later on by Hawking and Geroch (see Penrose–Hawking singularity theorems).