Nuprl Lemma : change-to-lemma 11,40

T:Type. 
(x,y:T. decidable((x = y)))
 (es:event_system{i:l}, e:es-E(es), x:Id.
 es-dtype(es; loc(e); xT)
  (e'e.es-when(esxe') = es-when(esxe T
   e'<e.@e'(xes-when(esxe))
    e''(e',e].es-when(esxe'') = es-when(esxe T)) 
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Definitionsx:AB(x), P  Q, es-dtype(esixT), P  Q, P  Q, es-locl(esee'), t  T, prop{i:l}, xt(x), A c B, ee'.P(e), T, True, guard(T), e<e'.P(e), x:AB(x), e(e1,e2].P(e), @e(xv), wellfounded{i:l}(Ax,y.R(x;y)), x(s), decidable(P), A, P  Q, False
Lemmases-locl-wellfnd, event system-level-subtype, assert wf, es-isconst wf, es-vartype wf, alle-le wf, member wf, Id wf, es-loc wf, es-E wf, es-locl wf, es-when wf, subtype rel self, existse-before wf, es-change-to wf, alle-between3 wf, not wf, es-first wf, es-dtype wf, es-causl wf, event system wf, decidable wf, decidable assert, es-le wf, es-le-iff, es-after wf, es-pred wf, es-loc-pred, es-pred-locl, es-after-pred2, es-locl transitivity2, es-le weakening, squash wf, true wf, es-locl-iff

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