fact: Fixpoint TraceInList (T : Trace) : list triplet -> Prop := fun L : list triplet => match T with | emptyTrace => True | tripletTrace t => In t L | seqTrace T1 T2 => TraceInList T1 L /\ TraceInList T2 L | dilemmaTrace a b T1 T2 => TraceInList T1 L /\ TraceInList T2 L end.