Very often in mathematics the crucial problem is to recognize and discover what are the relevant concepts; once this is accomplished the job may be more than half done.
Yitz Herstein
Good mathematicians see analogies between theorems. Great mathematicians see analogies between analogies.
Banach, in a 1957 letter to Ulam.
Yitz Herstein
Banach, in a 1957 letter to Ulam.