subst command in RPN mode (bug ?)

[Philippe]

Hello, 

To summarize, let :

Form1: subst(2*q , q=2)
Form2: subst(' 2*q ' , ' q=2 ')
Form3: subst(" 2*q " , "  q=2  ")
Form4: subst(" ' 2*q' " , " ' q=2 ' ")

BAT = Bad Argument Type error
SYN = Syntax error
n.a = not applicable

Then, we have :

1) In textbook entry, if q is not defined 

            |   Home   |    CAS
---------------------------------------------
Form1     |   SYN    |    4
Form2     |   SYN    |    4
Form3     |   4       |    BAT
Form4     |   4       |    BAT
---------------------------------------------

2) In textbook entry, if q is defined (0 in this case)

            |   Home                |    CAS
---------------------------------------------
Form1     |   BAT                 |    Warning, then 0
Form2     |   4                    |    4
Form3     |   0   (no warning)   |    BAT       
Form4     |   4                    |    BAT
---------------------------------------------

3) In RPN mode (forms are of course adapted), if q is not defined

            |   Home      |   
---------------------------------------------
Form1     |   n.a        |    
Form2     |   SYN       |    can't push '2*q' on stack
Form3     |   4          |    
Form4     |   4          |    
---------------------------------------------

4) In RPN mode, if q is defined (0 in this case)

            |   Home      |   
---------------------------------------------
Form1     |   n.a        |   
Form2     |   0          |    
Form3     |   0          |    
Form4     |   4          |    
---------------------------------------------

- In RPN, we cannot push expression that contains undefined variable:
  'q' Enter produce a syntax error. We already know that this is a big regression compared to hp50...hp28. No more comment.

- The Form2 seems (at least to me !) the most suited to have a homogeneous and clean syntax between Home view and CAS, RPN and algebraic notations.

- The warning "Warning, replacing 0 by 2, a substitution variable should perhaps be purged." is useful

- May be the electronic help should be updated (in order to explain simple/double quotes)

Cheers,
Philippe