theorem BFO.ObjectAggregate.At.toParent
theorem BFO.ObjectAggregate.At.toParent: ∀ (x t : Type) [At x t], MaterialEntity.At x t
theorem BFO.ObjectAggregate.At.toParent
theorem BFO.ObjectAggregate.At.toParent: ∀ (x t : Type) [At x t], MaterialEntity.At x t