
theorem Th80:
Sum digits(154,10) = 10
proof
  thus Sum digits(154,10) = Sum <%4,5%>+Sum <%1%> by Th79,AFINSQ_2:55
  .= (4 + 5) + Sum <%1%> by AFINSQ_2:54
  .= 9 + 1 by AFINSQ_2:53
  .= 10;
end;
