
theorem Th157:
Sum digits(210,10) = 3
proof
  thus Sum digits(210,10) = Sum <%0,1%>+Sum <%2%> by Th156,AFINSQ_2:55
  .= (0 + 1) + Sum <%2%> by AFINSQ_2:54
  .= 1 + 2 by AFINSQ_2:53
  .= 3;
end;
