
theorem Th1300:
Sum digits(4025,10) = 11
proof
  thus Sum digits(4025,10) = Sum <%5,2,0%>+Sum <%4%> by Th1299,AFINSQ_2:55
  .= Sum <%5,2%> + Sum <%0%> + Sum <%4%> by AFINSQ_2:55
  .= (5 + 2) + Sum <%0%> + Sum <%4%> by AFINSQ_2:54
  .= (5 + 2 + 0) + Sum <%4%> by AFINSQ_2:53
  .= 7 + 4 by AFINSQ_2:53
  .= 11;
end;
