
theorem Th513:
Sum digits(1840,10) = 13
proof
  thus Sum digits(1840,10) = Sum <%0,4,8%>+Sum <%1%> by Th512,AFINSQ_2:55
  .= Sum <%0,4%> + Sum <%8%> + Sum <%1%> by AFINSQ_2:55
  .= (0 + 4) + Sum <%8%> + Sum <%1%> by AFINSQ_2:54
  .= (0 + 4 + 8) + Sum <%1%> by AFINSQ_2:53
  .= 12 + 1 by AFINSQ_2:53
  .= 13;
end;
