
theorem Th431:
Sum digits(1020,10) = 3
proof
  thus Sum digits(1020,10) = Sum <%0,2,0%>+Sum <%1%> by Th430,AFINSQ_2:55
  .= Sum <%0,2%> + Sum <%0%> + Sum <%1%> by AFINSQ_2:55
  .= (0 + 2) + Sum <%0%> + Sum <%1%> by AFINSQ_2:54
  .= (0 + 2 + 0) + Sum <%1%> by AFINSQ_2:53
  .= 2 + 1 by AFINSQ_2:53
  .= 3;
end;
