public ReachabilityAnnotation(Reference reference, ReachabilityChain canReach)
     : this(new FixedSet <Reference>(reference.Yield()), canReach)
 {
 }
 public ReachabilityAnnotation(FixedSet <Reference> references, ReachabilityChain canReach)
     : base(references)
 {
     CanReach = canReach;
 }