
theorem Th1304:
Sum digits(4075,10) = 16
proof
  thus Sum digits(4075,10) = Sum <%5,7,0%>+Sum <%4%> by Th1303,AFINSQ_2:55
  .= Sum <%5,7%> + Sum <%0%> + Sum <%4%> by AFINSQ_2:55
  .= (5 + 7) + Sum <%0%> + Sum <%4%> by AFINSQ_2:54
  .= (5 + 7 + 0) + Sum <%4%> by AFINSQ_2:53
  .= 12 + 4 by AFINSQ_2:53
  .= 16;
end;
