S := A \in A => A \in S

##</code><code>##

  S \in S => S \in S

##</code><code>##

  R \notin R => R \in R

##</code><code>##

  S := (A = S | A \in A) => A \in S
  or S := (A != S & A \in A) => A \in S
  R := (A = R | A \notin A) => A \in R
  or R := (A != R & A \notin A) => A \in R