
theorem Th1290:
Sum digits(3875,10) = 23
proof
  thus Sum digits(3875,10) = Sum <%5,7,8%>+Sum <%3%> by Th1289,AFINSQ_2:55
  .= Sum <%5,7%> + Sum <%8%> + Sum <%3%> by AFINSQ_2:55
  .= (5 + 7) + Sum <%8%> + Sum <%3%> by AFINSQ_2:54
  .= (5 + 7 + 8) + Sum <%3%> by AFINSQ_2:53
  .= 20 + 3 by AFINSQ_2:53
  .= 23;
end;
