
theorem Th1000:
Sum digits(1104,10) = 6
proof
  thus Sum digits(1104,10) = Sum <%4,0,1%>+Sum <%1%> by Th999,AFINSQ_2:55
  .= Sum <%4,0%> + Sum <%1%> + Sum <%1%> by AFINSQ_2:55
  .= (4 + 0) + Sum <%1%> + Sum <%1%> by AFINSQ_2:54
  .= (4 + 0 + 1) + Sum <%1%> by AFINSQ_2:53
  .= 5 + 1 by AFINSQ_2:53
  .= 6;
end;
