
theorem Th667:
Sum digits(3380,10) = 14
proof
  thus Sum digits(3380,10) = Sum <%0,8,3%>+Sum <%3%> by Th666,AFINSQ_2:55
  .= Sum <%0,8%> + Sum <%3%> + Sum <%3%> by AFINSQ_2:55
  .= (0 + 8) + Sum <%3%> + Sum <%3%> by AFINSQ_2:54
  .= (0 + 8 + 3) + Sum <%3%> by AFINSQ_2:53
  .= 11 + 3 by AFINSQ_2:53
  .= 14;
end;
