code: public BitVector duplicate(boolean copy, boolean mutable) {
  		if (mutable && !copy && !this.mutable) throw new IllegalStateException("Cannot obtain mutable view of an immutable BitVector");
  		return duplicateAdj(start, finish, copy, mutable);
  	}
docs: Duplicates the {@link BitVector}.
  
  @param copy
  true if the duplicate should be a detached copy, false if it
  should be a view, backed by the same bit data.
  @param mutable
  whether the duplicate should be mutable
  @return a duplicate of this BitVector
  @see #duplicateRange(int, int, boolean, boolean)