
theorem Th1278:
Sum digits(3675,10) = 21
proof
  thus Sum digits(3675,10) = Sum <%5,7,6%>+Sum <%3%> by Th1277,AFINSQ_2:55
  .= Sum <%5,7%> + Sum <%6%> + Sum <%3%> by AFINSQ_2:55
  .= (5 + 7) + Sum <%6%> + Sum <%3%> by AFINSQ_2:54
  .= (5 + 7 + 6) + Sum <%3%> by AFINSQ_2:53
  .= 18 + 3 by AFINSQ_2:53
  .= 21;
end;
