
theorem Th39:
Sum digits(120,10) = 3
proof
  thus Sum digits(120,10) = Sum <%0,2%>+Sum <%1%> by Th38,AFINSQ_2:55
  .= (0 + 2) + Sum <%1%> by AFINSQ_2:54
  .= 2 + 1 by AFINSQ_2:53
  .= 3;
end;
