T:Type, eq:EqDecider(T), es:event_system{i:l}, x:Id, e:{e:es-E(es)| es-dtype(es; loc(e); x; T)} .
((x changed before e))  e'e.es-when(es; x; e') = es-when(es; x; e)  T 

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Definitions	True, if b then t else f fi , ff, tt, isl(x), b, A c B, x. t(x), P  Q, P  Q, es-dtype(es; i; x; T), EqDecider(T), prop{i:l}, P  Q, P  Q, t  T, change-to(x;e), x changed before e, P  Q, x:A. B(x), False, A, x(s)
Lemmas	false wf, true wf, alle-le wf, es-first wf, alle-between3 wf, es-when wf, es-change-to wf, existse-before wf, es-vartype wf, es-isconst wf, iff wf, bool wf, deq wf, event system wf, Id wf, es-loc wf, es-dtype wf, change-to wf, unit wf, es-E wf, isl wf, assert wf, not wf