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      Conway's field  of surreal
      numbers comes both with a natural total order and an additional
      “simplicity relation” which is also a partial order.
      Considering
 of surreal
      numbers comes both with a natural total order and an additional
      “simplicity relation” which is also a partial order.
      Considering  as a doubly
      ordered structure for these two orderings, an isomorphic copy of
 as a doubly
      ordered structure for these two orderings, an isomorphic copy of  into itself is called a
      surreal substructure. It turns out that many natural subclasses
      of
 into itself is called a
      surreal substructure. It turns out that many natural subclasses
      of  are actually of this
      type. In this paper, we study various constructions that give rise to
      surreal substructures and analyze important examples in greater detail.
 are actually of this
      type. In this paper, we study various constructions that give rise to
      surreal substructures and analyze important examples in greater detail.
    
      Authors: 
Keywords: surreal numbers, surreal substructures, group action, nested numbers