**ALGORITHM**: patternGrowth () |

**INPUT**: (1) : prefix sequence pattern. |

**OUTPUT**: the set of gap-constrained closed sequential |

patterns with prefix . |

(14)backward_check (P needPruning, hasBackwardExtension) |

(15)if (needPruning) |

(16)return; |

(17)forward_check(, hasForwardExtension); |

(18)if ! (hasBackwardExtension ∣∣ hasForwardExtension) |

(19)output pattern ; |

(20)search each forward space of all appearances of , and |

find the set of all local frequent items, ; |

(21)for each item in |

(22)build new pattern = + ; |

(23)call patternGrowth (); |

(24)return. |