
theorem Th437:
Sum digits(1080,10) = 9
proof
  thus Sum digits(1080,10) = Sum <%0,8,0%>+Sum <%1%> by Th436,AFINSQ_2:55
  .= Sum <%0,8%> + Sum <%0%> + Sum <%1%> by AFINSQ_2:55
  .= (0 + 8) + Sum <%0%> + Sum <%1%> by AFINSQ_2:54
  .= (0 + 8 + 0) + Sum <%1%> by AFINSQ_2:53
  .= 8 + 1 by AFINSQ_2:53
  .= 9;
end;
