
theorem Th457:
Sum digits(1280,10) = 11
proof
  thus Sum digits(1280,10) = Sum <%0,8,2%>+Sum <%1%> by Th456,AFINSQ_2:55
  .= Sum <%0,8%> + Sum <%2%> + Sum <%1%> by AFINSQ_2:55
  .= (0 + 8) + Sum <%2%> + Sum <%1%> by AFINSQ_2:54
  .= (0 + 8 + 2) + Sum <%1%> by AFINSQ_2:53
  .= 10 + 1 by AFINSQ_2:53
  .= 11;
end;
