
theorem Th1336:
Sum digits(4475,10) = 20
proof
  thus Sum digits(4475,10) = Sum <%5,7,4%>+Sum <%4%> by Th1335,AFINSQ_2:55
  .= Sum <%5,7%> + Sum <%4%> + Sum <%4%> by AFINSQ_2:55
  .= (5 + 7) + Sum <%4%> + Sum <%4%> by AFINSQ_2:54
  .= (5 + 7 + 4) + Sum <%4%> by AFINSQ_2:53
  .= 16 + 4 by AFINSQ_2:53
  .= 20;
end;
