
theorem Th219:
Sum digits(448,10) = 16
proof
  thus Sum digits(448,10) = Sum <%8,4%>+Sum <%4%> by Th218,AFINSQ_2:55
  .= (8 + 4) + Sum <%4%> by AFINSQ_2:54
  .= 12 + 4 by AFINSQ_2:53
  .= 16;
end;
