Rules that satisfy this property are said to be induced by G. 2 For example, rule (d) in Table 1 is valid according to GHKM, since the spans corresponding to 1 Note that we use a slightly different terminology.
2 an xRs rule ri is extracted from G by taking a subtree γ ∈ π as lhs(ri), appending a variable to each leaf node of γ that is internal to π, adding those variables to rhs(ri), ordering them in accordance to a, and if necessary inserting any word of f to ensure that rhs(ri) is a sequence of contiguous spans (e.g., [4][5][6] [7][8] for rule (f) in Table 1).