Re: multi-symbol variables

On 08/10/2021 04:09, David Farmer wrote:
>
> Taking this discussion out of GitHub.  I hope this is the right
> place.
>
> The important point which has arisen, which I believe we had not
> discussed previously, is how to mark a multi-letter string as
> representing a single variable.  For example, on this page:
>
> https://www.dummies.com/business/accounting/how-to-calculate-simple-and-compound-interest/ 
>
>
> it says
>
> Interest = p \times r \times t .
>
> Here "Interest" is an 8 character string which represents one
> quantity.
>
> This is analogous to the situation in our recent discussions,
> where B' is just one quantity which happens to be a string of
> two characters.  The fact that one of the characters is a prime
> is not the main issue.  I mentioned an example where a_1 was a
> (subscripted) string which also is really just a single variable.
>
> Prior to this week I don't think we had discussed the fact that
> B' is a 2-character quantity, while f' -- assuming that means the
> derivative of f -- is the object f on which ' is acting.
>
> The only point I am trying to make here is that we need a way to
> indicate that a collection of characters is really in indivisible
> unit which represents a single quantity.  The recent discussions were
> made more difficult by the fact that this had not been discussed
> previously.
>
> I suggest that " B' " should be handled the same way as " Interest "
> would be handled in the formula above.
>
> Regards,
>
> David Farmer
>
logically I agree that "B'" is the same as "Interest" but typographic 
details don't always follow logic,.


Interest is <mi>Interest</mi> which does the right thing automatically 
due to the rule about multi-letter mi using upright font. So it is easy 
in that case to say the default intent is the single name "Interest"


B'  is <msup><mi>B</mi><mo>&prime;</mo></msup> or arguably 
<msup><mi>B</mi><mo>'</mo></msup> or <mi>B'</mi>

Only the last of these has a natural intent as a single identifier (and 
traditionally mathml has been explicit that that form is not correct)


mathml's traditional solution to this was to allow presentation in 
content mathml token elements so

<ci><msup><mi>B</mi><mo>&prime;</mo></msup></ci>


is unambiguously a variable name B' but we are trying to do without 
content mathml here so..  I think the natural intent to use here would be


<msup intent="B prime"><mi>B</mi><mo>'</mo></msup> if the default intent 
on <mi>Interest</mi> is intent="Interest"


or


<msup intent="variable-name"><mi>B</mi><mo>'</mo></msup> if the default 
intent on <mi>Interest</mi> is intent="variable-name" (or some other 
known keyword to be decided) that means it's a variable and has natural 
reading just by reading the content.


David

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