$$A \to B,\,B \to CD$$

$$A \to B,\,B \to C.\,C \to D$$

$$AB \to C,\,C \to AD$$

$$A \to BCD$$

$$\left\{t \mid \exists u \in R_1\left(t[A] = u[A]\right) \land \neg \exists s \in R_2 \left(t[A] = s[A]\right)\right\}$$

$$\left\{ t \mid \forall u \in R_1\left(u[A]="x"\Rightarrow \exists s \in R_2\left(t[A] = s[A] \land s[A] = u[A]\right)\right) \right\}$$

$$\left\{t \mid \neg (t \in R_1)\right\}$$

$$\left\{t \mid \exists u \in R_1\left(t[A]=u[A]\right) \land \exists s \in R_2 \left(t[A] = s[A]\right)\right\}$$

$$ABE$$

$$DBC$$

$$DE5$$

$$9E7$$

$$xy + y'z$$

$$wx'y' + xy + xz$$

$$w'x + y'z + xy$$

$$xz+y$$