[FOM] lying to children

[T.Forster at dpmms.cam.ac.uk]

One such lie is the purported proof that a union of countably many 
countable sets is countable, when what is actually being proved is that a 
counted union of counted sets is counted (or that a countable union of 
counted sets is countable).

(For the incognescenti, a couinted set - a Conway-ism - is a countable set 
equippped with a counting.)

But no more of that: it is one of my hobby-horses. I would be interested in 
useful lies... i teach first-years...




On Oct 5 2011, Vaughan Pratt wrote:

>
>
>On 10/4/2011 8:22 AM, Timothy Y. Chow wrote:
>> As an aside, lying in calculus class is something we all do in one form 
>> or another so I don't think Nelson can be ethically faulted for doing 
>> so.
>
>Some of us who don't routinely teach calculus would find it interesting 
>to hear from those who do as to which "lies" are the most helpful in 
>getting students up to speed on the subject.  One could then judge which 
>ones are really necessary for good pedagogy, as opposed to being merely 
>unexamined conventional wisdom about the subject.
>
>Vaughan Pratt
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