Recall from Chapter 2.1 that a linear threshold function (abbreviated LTF) is a boolean-valued function $f : \{-1,1\}^n \to \{-1,1\}$ that can be represented as \begin{equation} \label{eqn:generic-LTF} f(x) = \mathrm{sgn}(a_0 + a_1 x_1 + \cdots + a_n x_n) \end{equation} for some constants $a_0, a_1, \dots, a_n \in {\mathbb R}$.

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Ryan O'Donnell: Yes, thanks! Sorry for the delay in replying.Ryan O'Donnell: No, it's definitely messed up. Will fix!Ryan O'Donnell: Thanks!Ryan O'Donnell: Hi Amir. It's just a 'dummy variable'; in some sense an X's...Ryan O'Donnell: Right, or I guess I can just switch 'codimension' to 'dimens...Ryan O'Donnell: Yep, thanks!Ryan O'Donnell: Thanks, seems like I spotted this one myself too. (Not corr...