
theorem Th909:
Sum digits(2288,10) = 20
proof
  thus Sum digits(2288,10) = Sum <%8,8,2%>+Sum <%2%> by Th908,AFINSQ_2:55
  .= Sum <%8,8%> + Sum <%2%> + Sum <%2%> by AFINSQ_2:55
  .= (8 + 8) + Sum <%2%> + Sum <%2%> by AFINSQ_2:54
  .= (8 + 8 + 2) + Sum <%2%> by AFINSQ_2:53
  .= 18 + 2 by AFINSQ_2:53
  .= 20;
end;
