
theorem Th903:
Sum digits(2222,10) = 8
proof
  thus Sum digits(2222,10) = Sum <%2,2,2%>+Sum <%2%> by Th902,AFINSQ_2:55
  .= Sum <%2,2%> + Sum <%2%> + Sum <%2%> by AFINSQ_2:55
  .= (2 + 2) + Sum <%2%> + Sum <%2%> by AFINSQ_2:54
  .= (2 + 2 + 2) + Sum <%2%> by AFINSQ_2:53
  .= 6 + 2 by AFINSQ_2:53
  .= 8;
end;
