Constructing the parse forest Earley's dissertation briefly describes an algorithm for constructing parse trees by adding a set of pointers from each non-terminal in an Earley item back to the items that caused it to be recognized. But Tomita noticed that this does not take into account the relations between symbols, so if we consider the grammar S → SS | b and the string bbb, it only notes that each S can match one or two b's, and thus produces spurious derivations for bb and bbbb as well as the two correct derivations for bbb.
constructing the parse forest earley's dissertation briefly describes an algorithm for constructing parse trees by adding a set of pointers from each non-terminal in an earley item back to the items that caused it to be recognized but tomita noticed that this does not take into account the relations between symbols so if we consider the grammar s → ss | b and the string bbb it only notes that each s can match one or two b's and thus produces spurious derivations for bb and bbbb as well as the two correct derivations for bbb