
theorem Th825:
Sum digits(1254,10) = 12
proof
  thus Sum digits(1254,10) = Sum <%4,5,2%>+Sum <%1%> by Th824,AFINSQ_2:55
  .= Sum <%4,5%> + Sum <%2%> + Sum <%1%> by AFINSQ_2:55
  .= (4 + 5) + Sum <%2%> + Sum <%1%> by AFINSQ_2:54
  .= (4 + 5 + 2) + Sum <%1%> by AFINSQ_2:53
  .= 11 + 1 by AFINSQ_2:53
  .= 12;
end;
