
theorem Th1210:
Sum digits(2550,10) = 12
proof
  thus Sum digits(2550,10) = Sum <%0,5,5%>+Sum <%2%> by Th1209,AFINSQ_2:55
  .= Sum <%0,5%> + Sum <%5%> + Sum <%2%> by AFINSQ_2:55
  .= (0 + 5) + Sum <%5%> + Sum <%2%> by AFINSQ_2:54
  .= (0 + 5 + 5) + Sum <%2%> by AFINSQ_2:53
  .= 10 + 2 by AFINSQ_2:53
  .= 12;
end;
