```uclid
/* Define module for the sequential circuit */
module main {
  /* Declare input, output and state variables */
  input x : boolean;
  output y : boolean;
  var r : boolean;

  /* Define initial state */
  init {
    r = false;
  }

  /* State transition rules */
  next(r) {
    r' = r || x; // next_r = x OR r
  }

  /* Output computation */
  define y {
    !(x ^ r) // y = NOT (x XOR r)
  }

  /* Define initial states as two separate states S1 and S2 */
  control {
    init (x == false && r == false) || (x == true && r == false);
  }

  /* LTL property to check if y is set to true infinitely often */
  property infinitely_often_y {
    G(F(y))
  }
}

/* Check the LTL property */
control {
  check;
  print_results;
}
```

In this code:
- `input x` represents the input variable x.
- `output y` represents the output variable y, defined as the negation of the XOR operation on x and r.
- `var r` is a register whose value in the next state (`next(r)`) depends on the current value of x and itself.
- We use `define y` for the computation of the output, y, from the current state's x and r values.
- The states are initialized using the control block with possible initial conditions `S1` (x = 0, r = 0) and `S2` (x = 1, r = 0).
- An LTL (linear temporal logic) property `infinitely_often_y` states the requirement that `y` should be true infinitely often, formalized as `G(F(y))` which is read as "Globally (always), it is eventually the case that (y)".
- The `control` block checks the LTL property and prints the results.