
theorem Th543:
Sum digits(2140,10) = 7
proof
  thus Sum digits(2140,10) = Sum <%0,4,1%>+Sum <%2%> by Th542,AFINSQ_2:55
  .= Sum <%0,4%> + Sum <%1%> + Sum <%2%> by AFINSQ_2:55
  .= (0 + 4) + Sum <%1%> + Sum <%2%> by AFINSQ_2:54
  .= (0 + 4 + 1) + Sum <%2%> by AFINSQ_2:53
  .= 5 + 2 by AFINSQ_2:53
  .= 7;
end;
