\begin{tikzpicture}[>=stealth']
  \matrix[column 1/.style={nodes={text width=9em,text ragged}}] at (-3,-1)
  {
    \node {$\mathsf{derived}\leq \mathsf{prefixable}$}; \\
    \node {$\mathsf{ready}\leq \mathsf{prefixable}$}; \\
  };
  \node (ded) at (0,-2) {$\mathsf{derived}$};
  \node (ened) at (2,-2) {$\mathsf{ready}$};
  \node (dened) at (1,0) {$\mathsf{prefixable}$};

  \draw[->] (ded) to (dened);
  \draw[->] (ened) to (dened);
\end{tikzpicture}

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