$LR(0)$ items

An $LR(0)$ item is a production rule with the marker `` ${}_{\triangle}$'' somewhere on the r.h.s.

An $LR(0)$ item of the form $A\, \rightarrow\, \alpha_1\alpha_2 \ldots \alpha_i {}_{\triangle} \alpha_{i+1} \ldots \alpha_n$ means that:

• we have already recognised terminal symbols on the input which correspond to (ie. which are reducible to) $\alpha_1 \alpha_2 \ldots \alpha_i$

• should we now recognise symbols corresponding to $\alpha_{i+1} \ldots \alpha_n$, then we will have moved to a final state in the DFA, and will be ready to reduce by the rule $A\, \rightarrow\, \alpha_1 \ldots \alpha_n$
  

Note that an item which has the `` ${}_{\triangle}$'' on the far right of the r.h.s. of a rule implies that it is time to perform a reduction by that rule (we've recognised everthing on the r.h.s.).