Intersection of $\emptyset$ and problem about listing definition of sets.

45 Views Asked by At

Definition: $A\cap B=\{x | x\in A \quad \text{and} \quad x\in B\}$

My problem appears when I try to apply this definition to empty sets as following:

$$\emptyset\cap \emptyset=\{x | x\in \emptyset \quad \text{and} \quad x\in \emptyset\}$$

Then I evaluate the proposition "$x\in \emptyset \quad \text{and} \quad x\in \emptyset$". If $x\in\emptyset$ is false then this has $0$ value.

That is:

$$x\in \emptyset \quad \text{and} \quad x\in \emptyset\equiv 0 \wedge 0\equiv 0$$

So what does $\emptyset\cap \emptyset=\{x \;| \; 0 \}$ mean?

In addition, generally, how we should consider the proposition written in the feature of the set $\{x\;|\; PROPOSITION \}$ when it comes proposition takes the value $0$ or $1$?