>>VFP has no '--' operator. It's valid arithmetic expression and result is correct.
>>
>>>* typo 3 => bad result (better a syntax error !)
>>>? 10--2
>
>I was not referring to the result, or '--' operator, but the syntax.
>
>It is a valid arithmetic expression?
>Depends on how you interpret the signs.
>
>I would prefer if every '--'.'-+','+-','++' I would return a syntax error.

Your preferences versus a century or two of consensus on mathematical syntax. Try this in other languages - a minus (and in some cases, plus) between any other operator and an expression means just that the sign of the expression is inverted (or isn't).

This has never been wrong. It's just that people aren't used to it, because they let their maths rust. Now you do the psychology.