 There are minimal degrees \(\mathbf{m}\)—i.e., degrees for which there is no \(\mathbf{a}\) such that \(\mathbf{0} &lt;_T \mathbf{a} &lt;_T \mathbf{m}\) (Sacks 1963b). Thus in general \(&lt;_T\) is not a dense order. (But by fact vii below, there are not minimal c.e. degrees.)