src/ZF/WF.thy
 author lcp Tue, 21 Jun 1994 17:20:34 +0200 changeset 435 ca5356bd315a parent 124 858ab9a9b047 child 930 63f02d32509e permissions -rw-r--r--
Addition of cardinals and order types, various tidying
```
(*  Title: 	ZF/wf.thy
ID:         \$Id\$
Author: 	Tobias Nipkow and Lawrence C Paulson

Well-founded Recursion
*)

WF = Trancl + "mono" + "equalities" +
consts
wf           :: "i=>o"
wf_on        :: "[i,i]=>o"			("wf[_]'(_')")

wftrec,wfrec :: "[i, i, [i,i]=>i] =>i"
wfrec_on     :: "[i, i, i, [i,i]=>i] =>i"	("wfrec[_]'(_,_,_')")
is_recfun    :: "[i, i, [i,i]=>i, i] =>o"
the_recfun   :: "[i, i, [i,i]=>i] =>i"

rules
(*r is a well-founded relation*)
wf_def	 "wf(r) == ALL Z. Z=0 | (EX x:Z. ALL y. <y,x>:r --> ~ y:Z)"

(*r is well-founded relation over A*)
wf_on_def      "wf_on(A,r) == wf(r Int A*A)"

is_recfun_def  "is_recfun(r,a,H,f) == \
\   			(f = (lam x: r-``{a}. H(x, restrict(f, r-``{x}))))"

the_recfun_def "the_recfun(r,a,H) == (THE f.is_recfun(r,a,H,f))"

wftrec_def  	 "wftrec(r,a,H) == H(a, the_recfun(r,a,H))"

(*public version.  Does not require r to be transitive*)
wfrec_def "wfrec(r,a,H) == wftrec(r^+, a, %x f. H(x, restrict(f,r-``{x})))"

wfrec_on_def   "wfrec[A](r,a,H) == wfrec(r Int A*A, a, H)"

end
```