3. The Rule in Action (continued)

The symbols continue to spread to the right of the CA space until it reached another o symbol in the CA space. It may be misleading in the example, but the reason the spreading to the right stops is because the condition in line 15 no longer applies. Not because the symbols have reached the edge of the screen. In TREND, there is no edge to the CA space. The symbols continue through to the other side without any break in the line.
The images below show the CA space at epoch 38 and 39.





At epoch 39, there are no more "dead" ctrl fields in the first row. So the condition in line 15 is no longer satisfied. So the statement in line 16 will no longer be executed.

So what happens at the next epoch?



At epoch 40, the symbols appear to move down the CA screen. The condition in bold in line 25 is now applicable at epoch 40.

25	if (no:ctrl==top:ctrl+1 || no:ctrl==0 && top:ctrl==225)
26	{
27	ctrl=no:ctrl+1;
28	sum=nw:cell+no:cell+ne:cell;
29	cell=table[sum];
30	}