
theorem Th525:
Sum digits(1960,10) = 16
proof
  thus Sum digits(1960,10) = Sum <%0,6,9%>+Sum <%1%> by Th524,AFINSQ_2:55
  .= Sum <%0,6%> + Sum <%9%> + Sum <%1%> by AFINSQ_2:55
  .= (0 + 6) + Sum <%9%> + Sum <%1%> by AFINSQ_2:54
  .= (0 + 6 + 9) + Sum <%1%> by AFINSQ_2:53
  .= 15 + 1 by AFINSQ_2:53
  .= 16;
end;
