PREFIX ex: <http://a.example>
PREFIX sx: <http://www.w3.org/ns/shex#>
PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>

[] a sx:Schema ;
  sx:shapes (<http://a.example/S1> <http://a.example/S2>
            <http://a.example/S3> <http://a.example/S4>) .

<http://a.example/S4> a sx:ShapeDecl ; sx:shapeExpr [ a sx:Shape ;
  sx:expression [ a sx:TripleConstraint ; sx:predicate <http://a.example/p5> ] ] .

<http://a.example/S1> a sx:ShapeDecl ; sx:shapeExpr [ a sx:Shape ;
  sx:expression [ a sx:EachOf ; sx:expressions (
    [ a sx:TripleConstraint ; sx:predicate <http://a.example/p1> ]
    [ a sx:TripleConstraint ; sx:predicate <http://a.example/p2> ;
      sx:min 0 ; sx:max 1 ;
      sx:valueExpr <http://a.example/S2> ]
  ) ] ] .

<http://a.example/S2> a sx:ShapeDecl ; sx:shapeExpr [ a sx:Shape ;
  sx:expression [ a sx:TripleConstraint ;
    sx:predicate <http://a.example/p3> ;
    sx:valueExpr <http://a.example/S3> ] ] .

<http://a.example/S3> a sx:ShapeDecl ; sx:shapeExpr [ a sx:Shape ;
  sx:expression [ a sx:TripleConstraint ;
    sx:predicate <http://a.example/p4> ;
    sx:valueExpr <http://a.example/S1> ] ] .