for k, n being Nat
for x being Tuple of n + 1,k -SD
for xn being Tuple of n,k -SD st ( for i being Nat st i in Seg n holds
x . i = xn . i ) holds
(SDDec xn) + (((Radix k) |^ n) * (DigA (x,(n + 1)))) = SDDec x