
theorem Th639:
Sum digits(3100,10) = 4
proof
  thus Sum digits(3100,10) = Sum <%0,0,1%>+Sum <%3%> by Th638,AFINSQ_2:55
  .= Sum <%0,0%> + Sum <%1%> + Sum <%3%> by AFINSQ_2:55
  .= (0 + 0) + Sum <%1%> + Sum <%3%> by AFINSQ_2:54
  .= (0 + 0 + 1) + Sum <%3%> by AFINSQ_2:53
  .= 1 + 3 by AFINSQ_2:53
  .= 4;
end;
