why cannot assign to function call

[Erik Max Francis]

Derek Martin wrote:
> On a mostly not related note: 
> 
> On Tue, Dec 30, 2008 at 07:52:26AM -0800, Aaron Brady wrote:
>> According to some rules, these are ungrammatical sentences, due to
>> plurality disagreement.  Ex:
>>
>> The Morning Star is ...
>> The Evening Star is ...
>> *The Morning Star and The Evening Star is...
>> *The Morning Star and The Evening Star are...
>>
>> Neither of the latter two is correct.  (* marks ungrammatical.)   As
>> such, the listener isn't sure what meaning to take.
> 
> This statement is false.  The latter of the two is grammatically
> correct.  The subject is a compound subject joined by the conjunction
> "and" which indicates that there are two subjects, and thus the plural
> form of the verb is necessary and correct.
>  
>> Identity isn't defined on math objects, only on Python objects; there
>> is no notion of 'is' in math.  
> 
> This is also false, it even has its own operator (which requires
> Unicode to display): ≡

That can mean a number of things, one of which means "is identically 
equal to," but identity means something different in mathematics than it 
means here.  In mathematics, identity means a relationship that is true 
regardless of the value of the variables involved (as opposed to 
equality which is only true under more specific circumstances).  In 
computer science, identity means that two expressions are represented by 
the same object, something which not only has no meaning in mathematics, 
but which should also be clear since mathematical identities need not 
have any individual variables on either side of the triple bar; take, 
for instance, the trigonometric identity

	cos^2 theta + sin^2 theta = 1.

Even if you write this equation with the triple bar to represent a 
mathematical identity (which it is), it obviously doesn't say anything 
about which "objects" are the same as each other.

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