
Can the difficulty of an exam be measured by how many bits of information a student would need to pass it? This may not be so absurd in the encyclopedic subjects but in mathematics it doesn't make any sense since things follow from each other and, in principle, whoever knows the bases knows everything. All of the results of a mathematical theorem are in the axioms of mathematics in embryonic form, aren't they?
Alfred Renyi 
If I feel unhappy, I do mathematics to become happy. If I am happy, I do mathematics to keep happy.
Alfred Renyi