I need to generate a transition state table. To do that, I find the combinations of rules that can be applied to a given rule. Before I can do that, note that nested rules are replaced by 'accented' values:
(tile: at (a (t)) r) becomes
(tile: at2 (t) t')
(tile: at (a t') r)
Hence, according to this, the (t) node can generate both r and t', and this is indistinguishable form the perspective of the (t) node.