
theorem Th120:
Sum digits(156,10) = 12
proof
  thus Sum digits(156,10) = Sum <%6,5%>+Sum <%1%> by Th119,AFINSQ_2:55
  .= (6 + 5) + Sum <%1%> by AFINSQ_2:54
  .= 11 + 1 by AFINSQ_2:53
  .= 12;
end;
