
theorem Th334:
Sum digits(646,10) = 16
proof
  thus Sum digits(646,10) = Sum <%6,4%>+Sum <%6%> by Th333,AFINSQ_2:55
  .= (6 + 4) + Sum <%6%> by AFINSQ_2:54
  .= 10 + 6 by AFINSQ_2:53
  .= 16;
end;
