code: @Override
  	public boolean isValid() {
  		if (_valid == null) {
  			final byte[] check = bit.newArray(_validAlleles.length());
  			_valid = _genes.forAll(g -> !getAndSet(check, g.getAlleleIndex()));
  		}
  
  		return _valid;
  	}
docs: Check if this chromosome represents still a valid permutation (or subset)
  of the given valid alleles.