[Lazarus] How can I increment/decrement a alphanumeric value?

[Antônio]

There is a problem wiht Num2Dec.

for
Hex := 'G'
Dec2Numb(Numb2Dec(Hex, 16) - 1, {Length(Hex)} 2, 16)  will not refuse
'G' as an invalid hexadecimal number. The result would be 'F'.

Antônio