code: def check_preorder_collision( self, preorder_hash, block_id, checked_ops ):
          
  
          return self.check_collision( "preorder_hash", preorder_hash, block_id, checked_ops, OPCODE_PREORDER_OPS )
docs: Are there any colliding preorders in this block?
          Set the '__collided__' flag and related flags if so, so we don't commit them.
  
          Not called directly; called by the @state_preorder() decorator in blockstack.lib.operations.preorder and blockstack.lib.operations.namespacepreorder