This is very often misunderstood. Rather, he comments on the current proof of the convergence of that series, which is accomplished by multiplying the series by a and subtracting afterwards. It is correctly derived, proved, and elegant in its brevity. While compelled to agree to the correctness of the above proceeding, there are many who feel dissatisfied, tricked. Mathematics does not operate with objects but with thoughts or ideas and makes the latter perceivable or observable as forms or diagrams.
Diagrams are models in the strict logical sense.
This definition, however, reappears also in the determination of formal logic and is summed up in the so-called immediacy claim for formal systems. Only the text, the sign, the formal can in the last instance, be given in a pure state and thus does not entail any further problems of meaning and justification. On this basis Hilbert had called formal logic a material logic. The starting point of this problem is the assumption that every proposition immediately implies itself. The difference between intuition and logic must thus be sought in other circumstances.