
theorem Th222:
Sum digits(17,10) = 8
proof
  thus Sum digits(17,10) = Sum <%7%>+Sum <%1%> by Th221,AFINSQ_2:55
  .= 7 + Sum <%1%> by AFINSQ_2:53
  .= 7+1 by AFINSQ_2:53
  .= 8;
end;
