internal DynamicPartition([NotNull] DynamicKeySubspace subspace)
 {
     Contract.Requires(subspace != null);
     this.Subspace = subspace;
 }
 internal DynamicKeys(DynamicKeySubspace parent, IDynamicKeyEncoder encoder)
 {
     Contract.Requires(parent != null && encoder != null);
     this.Parent  = parent;
     this.Encoder = encoder;
 }