code: //non-compiled with javac: Compilable with Java15
  package com.puppycrawl.tools.checkstyle.grammar.java15;
  
  public sealed class InputAstRegressionSealedAndPermits permits Circle, Square, Rectangle {
  }
  
  final class Circle extends InputAstRegressionSealedAndPermits implements Squircle {
  }
  
  sealed class Rectangle extends InputAstRegressionSealedAndPermits
      implements Cloneable
      permits TransparentRectangle, FilledRectangle {
  }
  
  final class TransparentRectangle extends Rectangle {
  }
  
  non-sealed class Square extends InputAstRegressionSealedAndPermits implements Squircle {
  }
  
  final class FilledRectangle extends Rectangle {
  }
  
  sealed interface Squircle permits Circle, Square {
  
  }
  
  class Tricky {
      public static void main(String[] args) {
          int non = 2;
          int sealed = 4;
          int permits = non - sealed;
      }
  }
  