
theorem Th663:
Sum digits(3340,10) = 10
proof
  thus Sum digits(3340,10) = Sum <%0,4,3%>+Sum <%3%> by Th662,AFINSQ_2:55
  .= Sum <%0,4%> + Sum <%3%> + Sum <%3%> by AFINSQ_2:55
  .= (0 + 4) + Sum <%3%> + Sum <%3%> by AFINSQ_2:54
  .= (0 + 4 + 3) + Sum <%3%> by AFINSQ_2:53
  .= 7 + 3 by AFINSQ_2:53
  .= 10;
end;
