 Completely independent from Gentzen, Jaśkowski (1934) described two methods. Of interest to us in this article is the one found in a lengthy footnote, where he describes a pictorial method that he had announced  earlier.[6]  The pictorial method involved the drawing of “boxes” around portions of a proof, to indicate that the enclosed formulas are “considered as following only under a supposition”—or as we might say, they are a subproof that follows from an assumed  premise.[7]