Hi Alex, I need your info about the citation you put on your writing of proof. There I find you quote the words of Vladimir Arnold. I am very interseted in that say and I would like to put in the beginning of chapter of my thesis about conceptions of mathematical proof. However, I did not find the source of that quotation except that it is said by Prof. Arnol. If you have any ideas about where and when he said that statement, could you please tell me.