**Problem Detail:**

Can anybody give me an idea how to write this assertion in in first order logic?

X has not passed one or more of the prerequisites for A.

Here, X is the name of a person and A is a constant representing a course name.

###### Asked By : robert

#### Answered By : Luke Mathieson

Expressing properties of elements of the universe in first order logic is mostly achieved through defining appropriate relations. So for this you might like to consider relations like:

- $P(x)$ - $x$ is a person,
- $C(x)$ - $x$ is a course,
- $Pre(x,y)$ - $x$ is a prerequisite of $y$ (note that this doesn't actually say that $x$ and $y$ are courses),
- $Pass(x,y)$ - $x$ has passed course $y$.

(The parentheses are just included for clarity - you may have seen different notation where relations are written without.)

Then the rest is just building the logical formula, which in this case should be fairly obvious.

$notready(x,a) \equiv P(x) \wedge C(a) \wedge \exists y(C(y) \wedge Pre(y,a) \wedge \neg Pass(x,y)) $

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Question Source : http://cs.stackexchange.com/questions/22060

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