
theorem Th1218:
Sum digits(2675,10) = 20
proof
  thus Sum digits(2675,10) = Sum <%5,7,6%>+Sum <%2%> by Th1217,AFINSQ_2:55
  .= Sum <%5,7%> + Sum <%6%> + Sum <%2%> by AFINSQ_2:55
  .= (5 + 7) + Sum <%6%> + Sum <%2%> by AFINSQ_2:54
  .= (5 + 7 + 6) + Sum <%2%> by AFINSQ_2:53
  .= 18 + 2 by AFINSQ_2:53
  .= 20;
end;
