Editing CYK algorithm (section)

===Generating a parse tree===
The above algorithm is a [[recognizer]] that will only determine if a sentence is in the language. It is simple to extend it into a [[parser]] that also constructs a [[parse tree]], by storing parse tree nodes as elements of the array, instead of the boolean 1. The node is linked to the array elements that were used to produce it, so as to build the tree structure. Only one such node in each array element is needed if only one parse tree is to be produced. However, if all parse trees of an ambiguous sentence  are to be kept, it is necessary to store in the array element a list of all the ways the corresponding node can be obtained in the parsing process. This is sometimes done with a second table B[n,n,r] of so-called ''backpointers''.
The end result is then a shared-forest of possible parse trees, where common trees parts are factored between the various parses. This shared forest can conveniently be read as an [[ambiguous grammar]] generating only the sentence parsed, but with the same ambiguity as the original grammar, and the same parse trees up to a very simple renaming of non-terminals, as shown by {{harvtxt|Lang|1994}}.