
theorem Th88:
Sum digits(198,10) = 18
proof
  thus Sum digits(198,10) = Sum <%8,9%>+Sum <%1%> by Th87,AFINSQ_2:55
  .= (8 + 9) + Sum <%1%> by AFINSQ_2:54
  .= 17 + 1 by AFINSQ_2:53
  .= 18;
end;
