
theorem Th627:
Sum digits(2980,10) = 19
proof
  thus Sum digits(2980,10) = Sum <%0,8,9%>+Sum <%2%> by Th626,AFINSQ_2:55
  .= Sum <%0,8%> + Sum <%9%> + Sum <%2%> by AFINSQ_2:55
  .= (0 + 8) + Sum <%9%> + Sum <%2%> by AFINSQ_2:54
  .= (0 + 8 + 9) + Sum <%2%> by AFINSQ_2:53
  .= 17 + 2 by AFINSQ_2:53
  .= 19;
end;
