
theorem Th891:
Sum digits(2068,10) = 16
proof
  thus Sum digits(2068,10) = Sum <%8,6,0%>+Sum <%2%> by Th890,AFINSQ_2:55
  .= Sum <%8,6%> + Sum <%0%> + Sum <%2%> by AFINSQ_2:55
  .= (8 + 6) + Sum <%0%> + Sum <%2%> by AFINSQ_2:54
  .= (8 + 6 + 0) + Sum <%2%> by AFINSQ_2:53
  .= 14 + 2 by AFINSQ_2:53
  .= 16;
end;
