Refinement checking and FDR
		n Traces n The set of the sequences of visible actions in all possible runs n Example:    A  =   a -> b -> c -> Stop [] b -> c -> a -> Stop    Tr(A)  =  { a.b.c, b.c.a }    B  =   a -> Stop ||| b -> c -> Stop    Tr(A)  =  { a.b.c, b.a.c, b.c.a } Note that A is less nondeterministic than B: A represents only a subset of the possible runs of B