I’ve heard this joke in another guise:<p>An engineer, a physicist, and a mathematician are sitting in a train compartment and travelling through some countryside. Presently they come upon a field, which contains a white sheep.<p>“Oh look, in this country sheep are white!”, exclaims the engineer.
“Oh, how unwarranted!”, exclaims the physicist “in this country, there exists a white sheep, on a specific field.”
The mathematician just tut-tuts and curses under his breath. “In this country there exists at least one field, wherein there exists at least one sheep, <i>at least one side of which is white</i>.”<p>Oh, and another great one I enjoy:<p>An engineer, a physicist, and a mathematician sign up for a psychology experiment. They are each locked in a room with a tin of baked beans, the idea being that they will have to figure out how to open the tin with no tools in order not to starve.<p>Sometime later, the experimenters check up on them.<p>First, they come to the engineer’s cell. There’s a contented engineer sitting in the corner, craters on the wall, and the shrapnel of a totally shredded can strewn around. They ask him what he did. “Oh, I just battered it up against the wall.” Fair enough, they think.<p>Next, they check in on the physicist. They find him somewhat dishevelled, the walls covered with scratched calculations, and a neatly severed can in the middle of the room. They ask him for his account. “Oh, I calculated that if I emitted a note on a certain pitch, resonance would eventually cleave the can in half. It took me some time to figure out the note, though.” Again, fair enough.<p>Finally they get to the mathematician, whom they find shrivelled up, sitting cross-legged on the floor in front of an intact can as if venerating it, muttering “<i>assume the can is open, assume the can is open</i>”.<p>:)