
theorem Th455:
Sum digits(1260,10) = 9
proof
  thus Sum digits(1260,10) = Sum <%0,6,2%>+Sum <%1%> by Th454,AFINSQ_2:55
  .= Sum <%0,6%> + Sum <%2%> + Sum <%1%> by AFINSQ_2:55
  .= (0 + 6) + Sum <%2%> + Sum <%1%> by AFINSQ_2:54
  .= (0 + 6 + 2) + Sum <%1%> by AFINSQ_2:53
  .= 8 + 1 by AFINSQ_2:53
  .= 9;
end;
