minecraft-datapacks/datapacks/armour_statues-2-6-0/data/as/predicates/savedpose_mainhand.json

{
  "condition": "minecraft:entity_properties",
  "entity": "this",
  "predicate": {
    "equipment": {
      "mainhand": {
        "item": "minecraft:written_book",
	    "nbt": "{datapack:ArmourStatuesV2, SavedPose:{} }"
      }
    }
  }
}