
theorem Th517:
Sum digits(1880,10) = 17
proof
  thus Sum digits(1880,10) = Sum <%0,8,8%>+Sum <%1%> by Th516,AFINSQ_2:55
  .= Sum <%0,8%> + Sum <%8%> + Sum <%1%> by AFINSQ_2:55
  .= (0 + 8) + Sum <%8%> + Sum <%1%> by AFINSQ_2:54
  .= (0 + 8 + 8) + Sum <%1%> by AFINSQ_2:53
  .= 16 + 1 by AFINSQ_2:53
  .= 17;
end;
