
theorem Th605:
Sum digits(2760,10) = 15
proof
  thus Sum digits(2760,10) = Sum <%0,6,7%>+Sum <%2%> by Th604,AFINSQ_2:55
  .= Sum <%0,6%> + Sum <%7%> + Sum <%2%> by AFINSQ_2:55
  .= (0 + 6) + Sum <%7%> + Sum <%2%> by AFINSQ_2:54
  .= (0 + 6 + 7) + Sum <%2%> by AFINSQ_2:53
  .= 13 + 2 by AFINSQ_2:53
  .= 15;
end;
