
theorem Th489:
Sum digits(1600,10) = 7
proof
  thus Sum digits(1600,10) = Sum <%0,0,6%>+Sum <%1%> by Th488,AFINSQ_2:55
  .= Sum <%0,0%> + Sum <%6%> + Sum <%1%> by AFINSQ_2:55
  .= (0 + 0) + Sum <%6%> + Sum <%1%> by AFINSQ_2:54
  .= (0 + 0 + 6) + Sum <%1%> by AFINSQ_2:53
  .= 6 + 1 by AFINSQ_2:53
  .= 7;
end;
