
theorem Th1272:
Sum digits(3575,10) = 20
proof
  thus Sum digits(3575,10) = Sum <%5,7,5%>+Sum <%3%> by Th1271,AFINSQ_2:55
  .= Sum <%5,7%> + Sum <%5%> + Sum <%3%> by AFINSQ_2:55
  .= (5 + 7) + Sum <%5%> + Sum <%3%> by AFINSQ_2:54
  .= (5 + 7 + 5) + Sum <%3%> by AFINSQ_2:53
  .= 17 + 3 by AFINSQ_2:53
  .= 20;
end;
