## 4.1 Overview

`pf_return_t` [enumerable type]

  > > `typedef enum { pf_failed,
  > > pf_entailed,
  > > pf_sleep } pf_return_t;`

  Return type of a propagation function.

`pf_fnct_t` [function type]

  > > `typedef pf_return_t (* pf_fnct_t)(int *, PEL_SuspVar * []);`

  Type of a propagation function. A propagation function takes an array of parameter indicies and an array of references to constrained variables (`(PEL_SuspVar *)`). It returns a value of type `pf_return_t`.