
theorem Th603:
Sum digits(2740,10) = 13
proof
  thus Sum digits(2740,10) = Sum <%0,4,7%>+Sum <%2%> by Th602,AFINSQ_2:55
  .= Sum <%0,4%> + Sum <%7%> + Sum <%2%> by AFINSQ_2:55
  .= (0 + 4) + Sum <%7%> + Sum <%2%> by AFINSQ_2:54
  .= (0 + 4 + 7) + Sum <%2%> by AFINSQ_2:53
  .= 11 + 2 by AFINSQ_2:53
  .= 13;
end;
