
theorem Th1308:
Sum digits(4125,10) = 12
proof
  thus Sum digits(4125,10) = Sum <%5,2,1%>+Sum <%4%> by Th1307,AFINSQ_2:55
  .= Sum <%5,2%> + Sum <%1%> + Sum <%4%> by AFINSQ_2:55
  .= (5 + 2) + Sum <%1%> + Sum <%4%> by AFINSQ_2:54
  .= (5 + 2 + 1) + Sum <%4%> by AFINSQ_2:53
  .= 8 + 4 by AFINSQ_2:53
  .= 12;
end;
