Merging EXCEPT statements

[jacky....@gmail.com]

Hello,

Suppose I have a function a, that has domain Z. Suppose x and y are in Z. 

I'm writing an action where both a[x] and a[y] must be changed.

I have one line of the following form:   

                   

  a' = [a EXCEPT ![x] = ...]

and another like so:                             

                     

 a' = [a EXCEPT ![y] = ...]

 How would I be able to write this altogether as one? Having both doesn't seem to work with Model Checking as count = 0 for those lines.

I apologize if I'm using the wrong terms to explain my problem. 

Thanks for any help

[Saksham Chand]

Try the following, as per equation (16.7) of Specifying systems:

a' = [a EXCEPT ![x] = X, ![y] = Y]

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[Stephan Merz]

Hi,

Saksham already pointed out how to update a function at several argument positions. Writing

/\ a' = [a EXCEPT ![x] = foo]

/\ a' = [a EXCEPT ![y] = bar]

implies that

[a EXCEPT ![x] = foo] = [a EXCEPT ![y] = bar]

which is unlikely to be true, which explains why you see line count 0 in TLC.

Stephan

[jacky....@gmail.com]

Thank-you Saksham!

On Tuesday, September 10, 2019 at 1:30:09 PM UTC-4, Saksham Chand wrote:

Try the following, as per equation (16.7) of Specifying systems:

a' = [a EXCEPT ![x] = X, ![y] = Y]

On Tue, Sep 10, 2019 at 1:03 PM <jacky....@gmail.com> wrote:

Hello,

Suppose I have a function a, that has domain Z. Suppose x and y are in Z. 

I'm writing an action where both a[x] and a[y] must be changed.

I have one line of the following form:   

                   

  a' = [a EXCEPT ![x] = ...]

and another like so:                             

                     

 a' = [a EXCEPT ![y] = ...]

 How would I be able to write this altogether as one? Having both doesn't seem to work with Model Checking as count = 0 for those lines.

I apologize if I'm using the wrong terms to explain my problem. 

Thanks for any help

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[jacky....@gmail.com]

Thanks for your explanation Stephan!

On Tuesday, September 10, 2019 at 1:33:07 PM UTC-4, Stephan Merz wrote:

Hi,

Saksham already pointed out how to update a function at several argument positions. Writing

/\ a' = [a EXCEPT ![x] = foo]

/\ a' = [a EXCEPT ![y] = bar]

implies that

[a EXCEPT ![x] = foo] = [a EXCEPT ![y] = bar]

which is unlikely to be true, which explains why you see line count 0 in TLC.

Stephan

On 10 Sep 2019, at 09:51, jacky....@gmail.com wrote:

Hello,

Suppose I have a function a, that has domain Z. Suppose x and y are in Z. 

I'm writing an action where both a[x] and a[y] must be changed.

I have one line of the following form:   

                   

  a' = [a EXCEPT ![x] = ...]

and another like so:                             

                     

 a' = [a EXCEPT ![y] = ...]

 How would I be able to write this altogether as one? Having both doesn't seem to work with Model Checking as count = 0 for those lines.

I apologize if I'm using the wrong terms to explain my problem. 

Thanks for any help

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