# Elementary Set Theory REPL

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## Help

X | Set names are in uppercase |

{x, 1} | Set members are in lowercase or are numeric |

univ | See what sets have been defined |

A = {1,2,3} | Define a set A that contains the elements 1,2,3 |

A + {4,5} | Union two sets |

A - {1,2} | Difference two sets |

A & B | Intersect two sets |

{a} in {a,b,c} | Asks if {a} is a subset of {a,b,c} |

{a} IN {a,b,c} | Asks if {a} is a proper subset of {a,b,c} |

A super B | Asks if A is the superset of B |

## Info

This webpage was built late one evening when a tweet by Jean Bezivin (@JBezivin) lead me to John Sowa's interesting page on what every Computer Scientist should know. I decided that readers of this article might benefit from some interactivity, and I also fancied refreshing my language design skills whilst playing about with making a REPL.

The simple language used in the REPL was created using jison, a Javascript implementation of Bison. The console is written entirely in Javascript. I've not obfuscated the code, so you are free to examine all of its inefficient glory.