
theorem Th519:
Sum digits(1900,10) = 10
proof
  thus Sum digits(1900,10) = Sum <%0,0,9%>+Sum <%1%> by Th518,AFINSQ_2:55
  .= Sum <%0,0%> + Sum <%9%> + Sum <%1%> by AFINSQ_2:55
  .= (0 + 0) + Sum <%9%> + Sum <%1%> by AFINSQ_2:54
  .= (0 + 0 + 9) + Sum <%1%> by AFINSQ_2:53
  .= 9 + 1 by AFINSQ_2:53
  .= 10;
end;
