
theorem Th481:
Sum digits(1520,10) = 8
proof
  thus Sum digits(1520,10) = Sum <%0,2,5%>+Sum <%1%> by Th480,AFINSQ_2:55
  .= Sum <%0,2%> + Sum <%5%> + Sum <%1%> by AFINSQ_2:55
  .= (0 + 2) + Sum <%5%> + Sum <%1%> by AFINSQ_2:54
  .= (0 + 2 + 5) + Sum <%1%> by AFINSQ_2:53
  .= 7 + 1 by AFINSQ_2:53
  .= 8;
end;
