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1 (* Title: ZF/perm |
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2 ID: $Id$ |
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3 Author: Lawrence C Paulson, Cambridge University Computer Laboratory |
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4 Copyright 1991 University of Cambridge |
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5 |
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6 The theory underlying permutation groups |
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7 -- Composition of relations, the identity relation |
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8 -- Injections, surjections, bijections |
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9 -- Lemmas for the Schroeder-Bernstein Theorem |
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10 *) |
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11 |
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12 Perm = ZF + |
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13 consts |
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14 O :: "[i,i]=>i" (infixr 60) |
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15 id :: "i=>i" |
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16 inj,surj,bij:: "[i,i]=>i" |
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17 |
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18 rules |
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19 |
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20 (*composition of relations and functions; NOT Suppes's relative product*) |
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21 comp_def "r O s == {xz : domain(s)*range(r) . \ |
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22 \ EX x y z. xz=<x,z> & <x,y>:s & <y,z>:r}" |
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23 |
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24 (*the identity function for A*) |
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25 id_def "id(A) == (lam x:A. x)" |
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26 |
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27 (*one-to-one functions from A to B*) |
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28 inj_def "inj(A,B) == { f: A->B. ALL w:A. ALL x:A. f`w=f`x --> w=x}" |
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29 |
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30 (*onto functions from A to B*) |
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31 surj_def "surj(A,B) == { f: A->B . ALL y:B. EX x:A. f`x=y}" |
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32 |
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33 (*one-to-one and onto functions*) |
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34 bij_def "bij(A,B) == inj(A,B) Int surj(A,B)" |
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35 |
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36 end |