I am teaching this year at Yale. Your letter has been sent to this address. I have tested the system in many lectures, I
asked the Auditors to guess what certain unknown symbols meant. People on a scientific level had no difficulties. I learned
some improvements from individual mistakes. It is surprising that less educated people or even scholars in the humanities
have the greatest trouble to [ . . . ] things.
I do not know a better way to introduce variables. Do not confuse unknowns (indicated by ?x . . . ) with variables. What
you represent are, to my opinion, unknowns, which have one value only (though unknown) not variables ranging over a certain
set. If, on the other hand, you mean to write 1 + a = 2 --> a =1, when the --> is omitted, you settle a syntax's
which I have never admitted throughout my exposition, viz. to omit connectives thus are the most essential part of the communication.
I thank you much for your interest and your bibliographical remark.