
theorem Th1302:
Sum digits(4050,10) = 9
proof
  thus Sum digits(4050,10) = Sum <%0,5,0%>+Sum <%4%> by Th1301,AFINSQ_2:55
  .= Sum <%0,5%> + Sum <%0%> + Sum <%4%> by AFINSQ_2:55
  .= (0 + 5) + Sum <%0%> + Sum <%4%> by AFINSQ_2:54
  .= (0 + 5 + 0) + Sum <%4%> by AFINSQ_2:53
  .= 5 + 4 by AFINSQ_2:53
  .= 9;
end;
