
theorem Th453:
Sum digits(1240,10) = 7
proof
  thus Sum digits(1240,10) = Sum <%0,4,2%>+Sum <%1%> by Th452,AFINSQ_2:55
  .= Sum <%0,4%> + Sum <%2%> + Sum <%1%> by AFINSQ_2:55
  .= (0 + 4) + Sum <%2%> + Sum <%1%> by AFINSQ_2:54
  .= (0 + 4 + 2) + Sum <%1%> by AFINSQ_2:53
  .= 6 + 1 by AFINSQ_2:53
  .= 7;
end;
