code: static <T> void crossover(
  		final MSeq<T> that,
  		final MSeq<T> other,
  		final int index
  	) {
  		assert index >= 0 :
  			format(
  				"Crossover index must be within [0, %d) but was %d",
  				that.length(), index
  			);
  
  		that.swap(index, min(that.length(), other.length()), other, index);
  	}
docs: Package private for testing purpose.