
theorem Th1280:
Sum digits(3725,10) = 17
proof
  thus Sum digits(3725,10) = Sum <%5,2,7%>+Sum <%3%> by Th1279,AFINSQ_2:55
  .= Sum <%5,2%> + Sum <%7%> + Sum <%3%> by AFINSQ_2:55
  .= (5 + 2) + Sum <%7%> + Sum <%3%> by AFINSQ_2:54
  .= (5 + 2 + 7) + Sum <%3%> by AFINSQ_2:53
  .= 14 + 3 by AFINSQ_2:53
  .= 17;
end;
