Collins parser is a parser that divides constituent into a non-terminal head, non-terminals that are on the left of the head, and non-terminals that are on the right of the head. Abstractly speaking, $LHS=L_n L_{n-1}...L_1 H R_1 ...R_{n-1}R_n$, where $L_i$, $H$ and $R_i$ are symbols that representing its category, head and head tag, such as VP(dumped, VP) in the “Workers dumped sacks into a bin.” example.