Примечание к статье "Функцiя Дiрiхле"
∀ x ( x ∈ R → ( x ∈ Q → D ( x ) = 1 ) ∧ ( x ∉ Q → D ( x ) = 0 ) ) {\displaystyle ~\forall x\ (x\in \mathbb {R} \ \to \ (x\in \mathbb {Q} \to D(x)=1)\ \land \ (x\notin \mathbb {Q} \to D(x)=0)\ )}
∀ x ( ( x ∈ Q → D ( x ) = 1 ) ∧ ( x ∈ R ∖ Q → D ( x ) = 0 ) ) {\displaystyle ~\forall x\ (\ (x\in \mathbb {Q} \to D(x)=1)\ \land \ (x\in \mathbb {R} \setminus \mathbb {Q} \to D(x)=0)\ )}
D = { ⟨ x , y ⟩ | ⟨ x , y ⟩ ∈ R 2 ∧ ( x ∈ Q → y = 1 ) ∧ ( x ∈ R ∖ Q → y = 0 ) } {\displaystyle ~\mathrm {D} =\{\langle x,y\rangle |\ \ \langle x,y\rangle \in \mathbb {R} ^{2}\ \land \ (x\in \mathbb {Q} \to y=1)\ \land \ (x\in \mathbb {R} \setminus \mathbb {Q} \to y=0)\}}
