src/ZF/ex/primrec0.thy
author wenzelm
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(*  Title: 	ZF/ex/primrec.thy
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    ID:         $Id$
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    Author: 	Lawrence C Paulson, Cambridge University Computer Laboratory
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    Copyright   1993  University of Cambridge
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Primitive Recursive Functions
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Proof adopted from
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Nora Szasz, 
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A Machine Checked Proof that Ackermann's Function is not Primitive Recursive,
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In: Huet & Plotkin, eds., Logical Environments (CUP, 1993), 317-338.
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See also E. Mendelson, Introduction to Mathematical Logic.
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(Van Nostrand, 1964), page 250, exercise 11.
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*)
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Primrec0 = ListFn +
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consts
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    SC      :: "i"
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    CONST   :: "i=>i"
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    PROJ    :: "i=>i"
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    COMP    :: "[i,i]=>i"
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    PREC    :: "[i,i]=>i"
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    primrec :: "i"
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    ACK	    :: "i=>i"
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    ack	    :: "[i,i]=>i"
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translations
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  "ack(x,y)"  == "ACK(x) ` [y]"
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rules
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  SC_def    "SC == lam l:list(nat).list_case(0, %x xs.succ(x), l)"
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  CONST_def "CONST(k) == lam l:list(nat).k"
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  PROJ_def  "PROJ(i) == lam l:list(nat). list_case(0, %x xs.x, drop(i,l))"
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  COMP_def  "COMP(g,fs) == lam l:list(nat). g ` map(%f. f`l, fs)"
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  (*Note that g is applied first to PREC(f,g)`y and then to y!*)
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  PREC_def  "PREC(f,g) == \
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\            lam l:list(nat). list_case(0, \
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\                      %x xs. rec(x, f`xs, %y r. g ` Cons(r, Cons(y, xs))), l)"
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  ACK_def   "ACK(i) == rec(i, SC, \
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\                      %z r. PREC (CONST (r`[1]), COMP(r,[PROJ(0)])))"
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end