The concept of compactor has been introduced in Kim et al. (2018) as a general data-reduction concept for parametrized counting problems. For a function $F:{\Sigma }^{\ast }\to \mathbb{N}$ and a parameterization $\kappa :{\Sigma }^{\ast }\to \mathbb{N}$, a compactor $(\mathsf{C},\mathsf{E})$ consists of a polynomial-time computable function $\mathsf{P}$, called condenser, and a computable function $\mathsf{M}$, called extractor, such that $F=\mathsf{M}\circ \mathsf{P}$. If the size of $\mathsf{P}\left(x\right)$ is bounded by a polynomial function of $\kappa \left(x\right)$, then we say that the compactor $(\mathsf{C},\mathsf{E})$ is of polynomial size. Compactors can be seen as an attempt to formalize the notion of preprocessing for counting problems.

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用于参数化计数问题的压实机

压实机的概念已在Kim等人中引入。（2018）作为参数化计数问题的通用数据精简概念。对于功能$F：{\Sigma }^{\ast }\to \mathbb{ñ}$ 和参数化 $\kappa ：{\Sigma }^{\ast }\to \mathbb{ñ}$压实机 $（\mathsf{C}，\mathsf{Ë}）$ 由多项式时间可计算函数组成 $\mathsf{P}$称为冷凝器和可计算函数$\mathsf{中号}$，称为提取器，这样$F=\mathsf{中号}\circ \mathsf{P}$。如果大小$\mathsf{P}（X）$ 由以下项的多项式函数限定 $\kappa （X）$，那么我们说压实机 $（\mathsf{C}，\mathsf{Ë}）$是多项式大小。压实机可以看作是对用于计数问题的预处理概念进行形式化的尝试。