
theorem Th1028:
Sum digits(1449,10) = 18
proof
  thus Sum digits(1449,10) = Sum <%9,4,4%>+Sum <%1%> by Th1027,AFINSQ_2:55
  .= Sum <%9,4%> + Sum <%4%> + Sum <%1%> by AFINSQ_2:55
  .= (9 + 4) + Sum <%4%> + Sum <%1%> by AFINSQ_2:54
  .= (9 + 4 + 4) + Sum <%1%> by AFINSQ_2:53
  .= 17 + 1 by AFINSQ_2:53
  .= 18;
end;
