
theorem Th839:
Sum digits(1430,10) = 8
proof
  thus Sum digits(1430,10) = Sum <%0,3,4%>+Sum <%1%> by Th838,AFINSQ_2:55
  .= Sum <%0,3%> + Sum <%4%> + Sum <%1%> by AFINSQ_2:55
  .= (0 + 3) + Sum <%4%> + Sum <%1%> by AFINSQ_2:54
  .= (0 + 3 + 4) + Sum <%1%> by AFINSQ_2:53
  .= 7 + 1 by AFINSQ_2:53
  .= 8;
end;
