schema Cloud {
	running : Bool

	sub create_vm (vm isref VM) {
		condition {
			this.running = true
			vm.created = false
		}
		effect {
			vm.in_cloud = this
			vm.created = true
		}
	}

	sub delete_vm (vm isref VM) {
		condition {
			this.running = true
			vm.created = true
			vm.in_cloud = this
		}
		effect {
			vm.created = false
			vm.in_cloud = null
		}
	}
}