
theorem Th1236:
Sum digits(2975,10) = 23
proof
  thus Sum digits(2975,10) = Sum <%5,7,9%>+Sum <%2%> by Th1235,AFINSQ_2:55
  .= Sum <%5,7%> + Sum <%9%> + Sum <%2%> by AFINSQ_2:55
  .= (5 + 7) + Sum <%9%> + Sum <%2%> by AFINSQ_2:54
  .= (5 + 7 + 9) + Sum <%2%> by AFINSQ_2:53
  .= 21 + 2 by AFINSQ_2:53
  .= 23;
end;
