Noncombustive Property
Three panels show a teacher naming 'obvious' facts like commutativity and continuity, each a warning that counterexamples are coming.
Content note: Mildly gruesome joke (brains catching fire).
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Free for classrooms, worksheets, slides and other non-commercial use under CC BY-NC 4.0, with credit to Ben Orlin.
Cartoon by Ben Orlin, Math with Bad Drawings. https://cartoons.mathwithbaddrawings.com/2017-09-04-noncombustive-property/ (CC BY-NC 4.0)Transcript
"Pro Tip: Whenever a mathematician assigns a name to a fact you've always taken for granted, things are about to get ugly."
[1] Teacher: "You know how 4×5 and 5×4 are the same? We call this 'commutativity.'" [board: two matrix products] Student: "Hmm..."
[2] Teacher: "So far, we've studied functions that can be drawn as a single curve. That's known as 'continuity.'" [board: a piecewise step function] Student: "why do I feel anxious about this"
[3] Teacher: "You notice how people's brains never catch fire all of a sudden, charring the insides of their skulls? We call this the 'noncombustive property.'" Student: "DON'T SAY IT"