Is it a list ?

[Marc Ernst Eddy van Woerkom]

>   Conjecture: I assume you meant to write [1, 2], which will give a 
>   well-formed list of the two numbers 1 and 2 :-)

Or [1|[2]] .. 

But why is is_list([1|2]) true?

Or asked differently, is there a legitimate use for ill-formed lists?

Regards,
Marc