
theorem Th809:
Sum digits(1056,10) = 12
proof
  thus Sum digits(1056,10) = Sum <%6,5,0%>+Sum <%1%> by Th808,AFINSQ_2:55
  .= Sum <%6,5%> + Sum <%0%> + Sum <%1%> by AFINSQ_2:55
  .= (6 + 5) + Sum <%0%> + Sum <%1%> by AFINSQ_2:54
  .= (6 + 5 + 0) + Sum <%1%> by AFINSQ_2:53
  .= 11 + 1 by AFINSQ_2:53
  .= 12;
end;
