 In setting up a formal system to capture, albeit necessarily only in part, logic as it figures in Brouwer’s foundations, naturally some priorly obtained meaning explanation is needed to serve as the criterion for intuitionistic validity. Yet none of the papers by Kolmogorov, Heyting, and Glivenko just mentioned made an explicit contribution to the meaning explanation of intuitionistic logic. As we will see, the explanations as given in the papers (which is not necessarily all their respective authors had in mind) were too vague for that. It is perhaps not surprising, then, that the systems were not equivalent; notably, Kolmogorov rejected Ex Falso, while Heyting and Glivenko accepted it. We will now discuss these papers in turn.