
theorem Th256:
Sum digits(391,10) = 13
proof
  thus Sum digits(391,10) = Sum <%1,9%>+Sum <%3%> by Th255,AFINSQ_2:55
  .= (1 + 9) + Sum <%3%> by AFINSQ_2:54
  .= 10 + 3 by AFINSQ_2:53
  .= 13;
end;
