
theorem Th503:
Sum digits(1740,10) = 12
proof
  thus Sum digits(1740,10) = Sum <%0,4,7%>+Sum <%1%> by Th502,AFINSQ_2:55
  .= Sum <%0,4%> + Sum <%7%> + Sum <%1%> by AFINSQ_2:55
  .= (0 + 4) + Sum <%7%> + Sum <%1%> by AFINSQ_2:54
  .= (0 + 4 + 7) + Sum <%1%> by AFINSQ_2:53
  .= 11 + 1 by AFINSQ_2:53
  .= 12;
end;
