“The fact that I have solved a problem is a purely subjective fact that in itself has as yet no general interest. However, the logical and mathematical problems possess the special property of the general validity of their solutions: If I have solved a logical or a mathematical problem, then I can present this solution in a way that is intelligible to all and it is necessary that it be recognized as a correct solution although this necessity has to a certain extent an ideal character, for it presupposes a sufficient intelligence on the part of the listener.”