diff --git a/examples/Chapter10.ipynb b/examples/Chapter10.ipynb new file mode 100644 index 0000000..fb5a4a1 --- /dev/null +++ b/examples/Chapter10.ipynb @@ -0,0 +1,253 @@ +{ + "cells": [ + { + "cell_type": "markdown", + "metadata": {}, + "source": [ + "# Programming the Kan theory\n", + "\n", + "## Introduction\n", + "\n", + "Let us recall some definitions in relation with the Kan simplicial sets.\n", + "\n", + "**Definition 1.** A Kan \"hat\" of dimension $n$ and index $i$ is a collection of $n$ simplices of dimension $(n-1)$, noted $(\\sigma_0, \\ldots, \\sigma_{i-1}, \\sigma_{i+1}, \\ldots, \\sigma_n)$, such that the following conditions are fulfilled:\n", + "$$ \\partial_j\\sigma_k=\\partial_k\\sigma_{j+1},\\quad k \\not= i,\\quad j+1 \\not= i, \\quad 0 \\leq j \\leq n-1, \\quad 0 \\leq k \\leq n-1, \\quad k \\leq j. $$\n", + "Note that there is no $\\sigma_i$ term in the list above; in a sense, the Kan process consists in constructing the missing $\\sigma_i$ to be considered as a \"composition\" of the given $\\sigma_j$'s.\n", + "\n", + "### Example\n", + "\n", + "We are going to work with the simplices of $\\Delta^\\mathbb{N}$. The set $(\\sigma_1, \\sigma_2) = $ ``((0 2), (0 1))`` is a Kan hat of dimension 2 and index 0. In effect, $\\delta_1\\sigma_1=\\delta_1\\sigma_2 =$ ``(0)``. Likewise, the two sets ``((1 2), (0 1))`` and ``((1 2), (0 2))`` are Kan hats of dimension 2 and of respective index 1 and 2. Of course, this definition applies equally if the simplices are degenerate.\n", + "\n", + "**Definition 2.** A *filling* of a Kan hat $(\\sigma_0, \\ldots, \\sigma_{i-1}, \\sigma_{i+1}, \\ldots, \\sigma_n)$, is an $n$-simplex $\\tilde{\\sigma}$, such that for every $j \\not= i$, $\\partial_j\\tilde{\\sigma}=\\sigma_j.$\n", + "\n", + "### Example\n", + "\n", + "A filling of ``((0 2), (0 1))`` is the 2-simplex ``(0 1 2)``. A filling of the Kan hat ``((1 1), (0 1))`` is the degenerate 2-simplex ``(0 1 1)``. A filling of the vertex ``(0)`` is the degenerate 1-simplex ``(0 0)``.\n", + "\n", + "**Definition 3.** A simplicial set is a Kan simplicial set if for every hat there exists a filling.\n", + "\n", + "### Representation of a Kan simplicial set\n", + "\n", + "A Kan simplicial set is implemented as an instance of the class ``KAN``, subclass of the class ``SIMPLICIAL-SET``.\n", + "\n", + "```lisp\n", + "(DEFCLASS KAN (simplicial-set)\n", + " ((kfll :type kfll :initarg :kfll :reader kfll1)))\n", + "```\n", + "\n", + "We recall that this new class inherits also from the class ``CHAIN-COMPLEX``. It has one slot of its own:\n", + "\n", + "``kfll``\n", + "> an object of type ``KFLL``, in fact a lisp function with 3 parameters describing a Kan hat: an index (an integer), a dimension (an integer) and the Kan hat (a list of abstract simplices). This function must return a filling of the Kan hat argument, i.e. an abstract simplex satisfying the theoritical definition.\n", + "\n", + "A printing method has been associated to the class ``KAN`` and the external representation of an instance is a string like ``[K``*n* ``Kan-Simplicial-Set]``, where *n* is the number plate of the Kenzo object.\n", + "\n", + "### Helpful functions on Kan simplicial sets\n", + "\n", + "``cat-init`` *[Function]*\n", + "> Clear in particular ``*Kan-list*``, the list of user created Kan simplicial sets and reset the global counter to 1.\n", + "\n", + "``Kan`` *n* *[Function]*\n", + "> Retrieve in the list ``*Kan-list*`` the Kan object instance whose the Kenzo identification is n. If it does not exist, return ``NIL``.\n", + "\n", + "``kfll &rest`` *args* *[Macro]*\n", + "> With only one argument (a Kan instance) return the slot ``kfll`` of this instance. With 4 arguments\n", + "like ``(kfll`` *kan indx dmns hat*``)``, return a filling of the Kan hat *hat*, of dimension *dmns*\n", + "and of index *indx* by applying the filling function value of the slot ``kfll`` of the Kan instance *kan*.\n", + "\n", + "``smst-kan`` *smst kfll* *[Function]*\n", + "> With the filling lisp function *kfll*, **transform** the simplicial set *smst* in an object of type ``KAN`` (in other word, *smst* is ``modified``). This is the easiest way to build a Kan simplicial set.\n", + "\n", + "``check-hat`` *kan indx dmns hat* *[Function]*\n", + "> Useful verification function to check if the collection of simplices ``hat`` is a valid Kan hat of dimension *dmns* and of index *indx* in the Kan simplicial set *kan*. In fact this works equally if *kan* is a general simplicial set.\n", + "\n", + "``check-kan`` *kan indx dmns hat* *[Function]*\n", + "> Useful verification function to check if the collection of simplices *hat* is a valid Kan hat of dimension *dmns* and of index *indx* in the Kan simplicial set *kan*. This verification function applies the filling function of the instance *kan* to the argument *hat* and perform the verification of the faces relations upon the resulting $dmns$-simplex.\n", + "\n", + "### Examples\n", + "\n", + "Let us take again the small examples of the introduction. First we define a function ``dkfll``, \n", + "a filling function suitable for a Kan hat in $\\Delta^\\mathbb{N}$. The user will note that in the abstract simplices the degeneracy operators and the geometric simplices are coded in binary." + ] + }, + { + "cell_type": "code", + "execution_count": null, + "metadata": { + "collapsed": false + }, + "outputs": [], + "source": [ + "(defun dkfll (indx dmns hat)\n", + " (cond ((= 1 dmns)\n", + " (absm 1 (gmsm (first hat))))\n", + " ((= 0 indx)\n", + " (let ((del-1 (absm-int-ext (first hat)))\n", + " (del-2 (absm-int-ext (second hat))))\n", + " (absm-ext-int\n", + " (cons (first del-1)\n", + " (cons (second del-2) (rest del-1))))))\n", + " ((= 1 indx)\n", + " (let ((del-0 (absm-int-ext (first hat)))\n", + " (del-2 (absm-int-ext (second hat))))\n", + " (absm-ext-int\n", + " (cons (first del-2) del-0))))\n", + " (t\n", + " (let ((del-0 (absm-int-ext (first hat)))\n", + " (del-1 (absm-int-ext (second hat))))\n", + " (absm-ext-int\n", + " (cons (first del-1) del-0))))))" + ] + }, + { + "cell_type": "code", + "execution_count": null, + "metadata": { + "collapsed": false + }, + "outputs": [], + "source": [ + "(def d (delta-infinity))" + ] + }, + { + "cell_type": "code", + "execution_count": null, + "metadata": { + "collapsed": false + }, + "outputs": [], + "source": [ + "(smst-kan d #'dkfll)" + ] + }, + { + "cell_type": "code", + "execution_count": null, + "metadata": { + "collapsed": false + }, + "outputs": [], + "source": [ + "(kfll d 0 1 (list (absm 0 1)))" + ] + }, + { + "cell_type": "code", + "execution_count": null, + "metadata": { + "collapsed": false + }, + "outputs": [], + "source": [ + "(kfll d 0 2 (list (absm 0 5) (absm 0 3)))" + ] + }, + { + "cell_type": "code", + "execution_count": null, + "metadata": { + "collapsed": false + }, + "outputs": [], + "source": [ + "(kfll d 1 2 (list (absm 0 6) (absm 0 3)))" + ] + }, + { + "cell_type": "code", + "execution_count": null, + "metadata": { + "collapsed": false + }, + "outputs": [], + "source": [ + "(kfll d 2 2 (list (absm 0 6) (absm 0 5)))" + ] + }, + { + "cell_type": "code", + "execution_count": null, + "metadata": { + "collapsed": false + }, + "outputs": [], + "source": [ + "(kfll d 0 2 (list (absm 0 3) (absm 0 3)))" + ] + }, + { + "cell_type": "code", + "execution_count": null, + "metadata": { + "collapsed": false + }, + "outputs": [], + "source": [ + "(kfll d 1 2 (list (absm 1 2) (absm 0 3)))" + ] + }, + { + "cell_type": "code", + "execution_count": null, + "metadata": { + "collapsed": false + }, + "outputs": [], + "source": [ + "(check-hat d 1 2 (list (absm 1 2) (absm 0 3)))" + ] + }, + { + "cell_type": "code", + "execution_count": null, + "metadata": { + "collapsed": false + }, + "outputs": [], + "source": [ + "(check-hat d 0 1 (list (absm 0 1)))" + ] + }, + { + "cell_type": "code", + "execution_count": null, + "metadata": { + "collapsed": false + }, + "outputs": [], + "source": [ + "(check-kan d 0 1 (list (absm 0 1)))" + ] + }, + { + "cell_type": "markdown", + "metadata": {}, + "source": [ + "More elaborate examples with Kan simplicial sets will be given later in the loop spaces chapter.\n", + "\n", + "### Lisp files concerned in this chapter\n", + "\n", + "``kan.lisp``.\n", + "\n", + "[``classes.lisp``, ``macros.lisp``, ``various.lisp``]." + ] + } + ], + "metadata": { + "kernelspec": { + "display_name": "SBCL Lisp", + "language": "lisp", + "name": "lisp" + }, + "language_info": { + "codemirror_mode": "text/x-common-lisp", + "mimetype": "text/x-common-lisp", + "name": "common-lisp", + "pygments_lexer": "common-lisp", + "version": "X3J13" + } + }, + "nbformat": 4, + "nbformat_minor": 0 +}