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The propositional formula given by the tree:

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  1. $\land \lor x_2 \lor x_1 \lnot x_1 \lnot x_1$
  2. $(x_2\lor x_2)\land (x_1\lor x_1)$
  3. $(\lnot x_1 \lor x_2)\land (\lnot x_1 \lor x_2)$
  4. None of these

My attempt :

I googled and I guessed this should be option $(3)\space (\lnot x_1 \lor x_2)\land (\lnot x_1 \lor x_2)$

My question is :

$x_1$ should be right child of $\lnot$ in both subtree?

Can you explain it, please?

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  • $\begingroup$ $\neg$ is a unary operator. In the tree it doesn't belong in a left or right child, because there are no left or right children to begin with. $\endgroup$ Commented Sep 23, 2016 at 11:52
  • $\begingroup$ @ParclyTaxel, exactly. thanks. $\endgroup$ Commented Sep 23, 2016 at 11:54
  • $\begingroup$ @ParclyTaxel, do you like your comment as answer, please answer it. $\endgroup$ Commented Sep 23, 2016 at 12:01
  • $\begingroup$ It is a PROpositional formula, from proposition. $\endgroup$ Commented Sep 23, 2016 at 12:17

1 Answer 1

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(Lifting my comment into an answer.)

$\neg$ is a unary operator, and hence does not have "left" and "right" children in a propositional tree. It just has a single child.

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  • $\begingroup$ Thanks for nice explanation. $\endgroup$ Commented Sep 23, 2016 at 12:09

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