Three professors are having lunch. One is from the computer engineering department, one from theoretical mathematics, and the third from philosophy.
The engineering prof is complaining, "Doing research in computer engineering is really expensive these days! All that expensive equipment really strains the budget."
"Poor fellow," says the mathematician, rather smugly. "All we really need for our research is a pencil, a pad of paper, and an eraser."
"Humph!" responds the philosopher. "We don't even need the eraser."