
theorem Th429:
Sum digits(1000,10) = 1
proof
  thus Sum digits(1000,10) = Sum <%0,0,0%>+Sum <%1%> by Th428,AFINSQ_2:55
  .= Sum <%0,0%> + Sum <%0%> + Sum <%1%> by AFINSQ_2:55
  .= (0 + 0) + Sum <%0%> + Sum <%1%> by AFINSQ_2:54
  .= (0 + 0 + 0) + Sum <%1%> by AFINSQ_2:53
  .= 1 by AFINSQ_2:53;
end;
