Accordingly, we use variables x A i ,e j ,l and x A i ,e j ,r , for each e j ∈ E(v i ), to denote the string components in tuples generated by A i (here subscripts l and r indicate left and right positions, respectively; see below).
the fact that variables in queries arising from LCFRS rules correspond to the endpoints of spans in the string to be parsed means that these queries have certain structural properties (Gildea, 2011).