
theorem Th189:
Sum digits(144,10) = 9
proof
  thus Sum digits(144,10) = Sum <%4,4%>+Sum <%1%> by Th188,AFINSQ_2:55
  .= (4 + 4) + Sum <%1%> by AFINSQ_2:54
  .= 8 + 1 by AFINSQ_2:53
  .= 9;
end;
