
theorem Th631:
Sum digits(3020,10) = 5
proof
  thus Sum digits(3020,10) = Sum <%0,2,0%>+Sum <%3%> by Th630,AFINSQ_2:55
  .= Sum <%0,2%> + Sum <%0%> + Sum <%3%> by AFINSQ_2:55
  .= (0 + 2) + Sum <%0%> + Sum <%3%> by AFINSQ_2:54
  .= (0 + 2 + 0) + Sum <%3%> by AFINSQ_2:53
  .= 2 + 3 by AFINSQ_2:53
  .= 5;
end;
