 While at least some of Bolzano’s mathematical work was influential during the nineteenth century, his logic met mostly with indifference and incomprehension. It was only towards the end of the century that philosophers, notably Kerry, Twardowski, Meinong, and Husserl, began to appreciate his achievements. Curiously, Frege, whose ideas were often so close to those of Bolzano and who in his time was one of the few logicians capable of understanding him, never mentions him in any of his publications or surviving papers. He was confronted with Bolzano’s ideas at least three times: in one of Kerry’s articles, in correspondence with Husserl, and later in the controversy with Korselt. We know of no evidence that he ever reacted to their allusions, and it is quite possible that he never laid hands on any of Bolzano’s works. Another interesting coincidence was noted by Mancosu (1996, 110–117 and note 69, p. 234): in §530 of TS, Bolzano argues that every indirect proof can be transformed into a direct proof. Mancosu points out the striking similarity of this claim with one to the same effect presented by Frege in one of his posthumous writings (“Logic in Mathematics”). In addition, Bolzano and Frege chose the very same example (Euclid I.19) to illustrate their claims.