Re: PARI/GP wrong on 7!!+7+1 being not prime, or oeis.org/Mathematica?

On 2025-08-28 19:59, Bill Allombert wrote:
> On Thu, Aug 28, 2025 at 05:02:28PM +0200, [email protected] 
> wrote:
>> Are you in the mood of adding another operator (!!) to GP?
> 
> Adding this one would break backward compatibility, so this is not
> an option.
> 
> ? 3!!
> %1 = 720
> 
> Cheers,
> Bill
> 
Understood — but we live in a world of unicode since more than 3 decades 
now.

Double exclamation mark is U+203C:
https://unicodeplus.com/U+203C

Current GP does not allow for it to be used as function name:

? ‼(x)=2*x;
   ***   syntax error, unexpected invalid token, expecting end of file: 
‼(x)=2*x;
   ***                                                                  
^-----------
?

But you could add it as operator ...

Regards,

Hermann.