
theorem Th1314:
Sum digits(4200,10) = 6
proof
  thus Sum digits(4200,10) = Sum <%0,0,2%>+Sum <%4%> by Th1313,AFINSQ_2:55
  .= Sum <%0,0%> + Sum <%2%> + Sum <%4%> by AFINSQ_2:55
  .= (0 + 0) + Sum <%2%> + Sum <%4%> by AFINSQ_2:54
  .= (0 + 0 + 2) + Sum <%4%> by AFINSQ_2:53
  .= 2 + 4 by AFINSQ_2:53
  .= 6;
end;
