
theorem Th573:
Sum digits(2440,10) = 10
proof
  thus Sum digits(2440,10) = Sum <%0,4,4%>+Sum <%2%> by Th572,AFINSQ_2:55
  .= Sum <%0,4%> + Sum <%4%> + Sum <%2%> by AFINSQ_2:55
  .= (0 + 4) + Sum <%4%> + Sum <%2%> by AFINSQ_2:54
  .= (0 + 4 + 4) + Sum <%2%> by AFINSQ_2:53
  .= 8 + 2 by AFINSQ_2:53
  .= 10;
end;
