Theorem istopclsd 37263

Description: A closure function which satisfies sscls 20860, clsidm 20871, cls0 20884, and clsun 32323 defines a (unique) topology which it is the closure function on. (Contributed by Stefan O'Rear, 1-Feb-2015.)

Hypotheses

Ref	Expression
istopclsd.b	⊢ (𝜑 → 𝐵 ∈ 𝑉)
istopclsd.f	⊢ (𝜑 → 𝐹:𝒫 𝐵⟶𝒫 𝐵)
istopclsd.e	⊢ ((𝜑 ∧ 𝑥 ⊆ 𝐵) → 𝑥 ⊆ (𝐹‘𝑥))
istopclsd.i	⊢ ((𝜑 ∧ 𝑥 ⊆ 𝐵) → (𝐹‘(𝐹‘𝑥)) = (𝐹‘𝑥))
istopclsd.z	⊢ (𝜑 → (𝐹‘∅) = ∅)
istopclsd.u	⊢ ((𝜑 ∧ 𝑥 ⊆ 𝐵 ∧ 𝑦 ⊆ 𝐵) → (𝐹‘(𝑥 ∪ 𝑦)) = ((𝐹‘𝑥) ∪ (𝐹‘𝑦)))
istopclsd.j	⊢ 𝐽 = {𝑧 ∈ 𝒫 𝐵 ∣ (𝐹‘(𝐵 ∖ 𝑧)) = (𝐵 ∖ 𝑧)}

Assertion

Ref	Expression
istopclsd	⊢ (𝜑 → (𝐽 ∈ (TopOn‘𝐵) ∧ (cls‘𝐽) = 𝐹))

Distinct variable groups:   𝑥,𝐵,𝑦,𝑧   𝜑,𝑥,𝑦,𝑧   𝑥,𝐹,𝑦,𝑧   𝑥,𝐽,𝑦   𝑥,𝑉,𝑦,𝑧

Allowed substitution hint:   𝐽(𝑧)

Proof of Theorem istopclsd

Step	Hyp	Ref	Expression
1		istopclsd.j	. . . 4 ⊢ 𝐽 = {𝑧 ∈ 𝒫 𝐵 ∣ (𝐹‘(𝐵 ∖ 𝑧)) = (𝐵 ∖ 𝑧)}
2		istopclsd.f	. . . . . . . . 9 ⊢ (𝜑 → 𝐹:𝒫 𝐵⟶𝒫 𝐵)
3		ffn 6045	. . . . . . . . 9 ⊢ (𝐹:𝒫 𝐵⟶𝒫 𝐵 → 𝐹 Fn 𝒫 𝐵)
4	2, 3	syl 17	. . . . . . . 8 ⊢ (𝜑 → 𝐹 Fn 𝒫 𝐵)
5	4	adantr 481	. . . . . . 7 ⊢ ((𝜑 ∧ 𝑧 ∈ 𝒫 𝐵) → 𝐹 Fn 𝒫 𝐵)
6		difss 3737	. . . . . . . . 9 ⊢ (𝐵 ∖ 𝑧) ⊆ 𝐵
7		istopclsd.b	. . . . . . . . . 10 ⊢ (𝜑 → 𝐵 ∈ 𝑉)
8		elpw2g 4827	. . . . . . . . . 10 ⊢ (𝐵 ∈ 𝑉 → ((𝐵 ∖ 𝑧) ∈ 𝒫 𝐵 ↔ (𝐵 ∖ 𝑧) ⊆ 𝐵))
9	7, 8	syl 17	. . . . . . . . 9 ⊢ (𝜑 → ((𝐵 ∖ 𝑧) ∈ 𝒫 𝐵 ↔ (𝐵 ∖ 𝑧) ⊆ 𝐵))
10	6, 9	mpbiri 248	. . . . . . . 8 ⊢ (𝜑 → (𝐵 ∖ 𝑧) ∈ 𝒫 𝐵)
11	10	adantr 481	. . . . . . 7 ⊢ ((𝜑 ∧ 𝑧 ∈ 𝒫 𝐵) → (𝐵 ∖ 𝑧) ∈ 𝒫 𝐵)
12		fnelfp 6441	. . . . . . 7 ⊢ ((𝐹 Fn 𝒫 𝐵 ∧ (𝐵 ∖ 𝑧) ∈ 𝒫 𝐵) → ((𝐵 ∖ 𝑧) ∈ dom (𝐹 ∩ I ) ↔ (𝐹‘(𝐵 ∖ 𝑧)) = (𝐵 ∖ 𝑧)))
13	5, 11, 12	syl2anc 693	. . . . . 6 ⊢ ((𝜑 ∧ 𝑧 ∈ 𝒫 𝐵) → ((𝐵 ∖ 𝑧) ∈ dom (𝐹 ∩ I ) ↔ (𝐹‘(𝐵 ∖ 𝑧)) = (𝐵 ∖ 𝑧)))
14	13	bicomd 213	. . . . 5 ⊢ ((𝜑 ∧ 𝑧 ∈ 𝒫 𝐵) → ((𝐹‘(𝐵 ∖ 𝑧)) = (𝐵 ∖ 𝑧) ↔ (𝐵 ∖ 𝑧) ∈ dom (𝐹 ∩ I )))
15	14	rabbidva 3188	. . . 4 ⊢ (𝜑 → {𝑧 ∈ 𝒫 𝐵 ∣ (𝐹‘(𝐵 ∖ 𝑧)) = (𝐵 ∖ 𝑧)} = {𝑧 ∈ 𝒫 𝐵 ∣ (𝐵 ∖ 𝑧) ∈ dom (𝐹 ∩ I )})
16	1, 15	syl5eq 2668	. . 3 ⊢ (𝜑 → 𝐽 = {𝑧 ∈ 𝒫 𝐵 ∣ (𝐵 ∖ 𝑧) ∈ dom (𝐹 ∩ I )})
17		istopclsd.e	. . . . . 6 ⊢ ((𝜑 ∧ 𝑥 ⊆ 𝐵) → 𝑥 ⊆ (𝐹‘𝑥))
18		simp1 1061	. . . . . . . . 9 ⊢ ((𝜑 ∧ 𝑥 ⊆ 𝐵 ∧ 𝑦 ⊆ 𝑥) → 𝜑)
19		simp2 1062	. . . . . . . . 9 ⊢ ((𝜑 ∧ 𝑥 ⊆ 𝐵 ∧ 𝑦 ⊆ 𝑥) → 𝑥 ⊆ 𝐵)
20		simp3 1063	. . . . . . . . . 10 ⊢ ((𝜑 ∧ 𝑥 ⊆ 𝐵 ∧ 𝑦 ⊆ 𝑥) → 𝑦 ⊆ 𝑥)
21	20, 19	sstrd 3613	. . . . . . . . 9 ⊢ ((𝜑 ∧ 𝑥 ⊆ 𝐵 ∧ 𝑦 ⊆ 𝑥) → 𝑦 ⊆ 𝐵)
22		istopclsd.u	. . . . . . . . 9 ⊢ ((𝜑 ∧ 𝑥 ⊆ 𝐵 ∧ 𝑦 ⊆ 𝐵) → (𝐹‘(𝑥 ∪ 𝑦)) = ((𝐹‘𝑥) ∪ (𝐹‘𝑦)))
23	18, 19, 21, 22	syl3anc 1326	. . . . . . . 8 ⊢ ((𝜑 ∧ 𝑥 ⊆ 𝐵 ∧ 𝑦 ⊆ 𝑥) → (𝐹‘(𝑥 ∪ 𝑦)) = ((𝐹‘𝑥) ∪ (𝐹‘𝑦)))
24		ssequn2 3786	. . . . . . . . . . 11 ⊢ (𝑦 ⊆ 𝑥 ↔ (𝑥 ∪ 𝑦) = 𝑥)
25	24	biimpi 206	. . . . . . . . . 10 ⊢ (𝑦 ⊆ 𝑥 → (𝑥 ∪ 𝑦) = 𝑥)
26	25	3ad2ant3 1084	. . . . . . . . 9 ⊢ ((𝜑 ∧ 𝑥 ⊆ 𝐵 ∧ 𝑦 ⊆ 𝑥) → (𝑥 ∪ 𝑦) = 𝑥)
27	26	fveq2d 6195	. . . . . . . 8 ⊢ ((𝜑 ∧ 𝑥 ⊆ 𝐵 ∧ 𝑦 ⊆ 𝑥) → (𝐹‘(𝑥 ∪ 𝑦)) = (𝐹‘𝑥))
28	23, 27	eqtr3d 2658	. . . . . . 7 ⊢ ((𝜑 ∧ 𝑥 ⊆ 𝐵 ∧ 𝑦 ⊆ 𝑥) → ((𝐹‘𝑥) ∪ (𝐹‘𝑦)) = (𝐹‘𝑥))
29		ssequn2 3786	. . . . . . 7 ⊢ ((𝐹‘𝑦) ⊆ (𝐹‘𝑥) ↔ ((𝐹‘𝑥) ∪ (𝐹‘𝑦)) = (𝐹‘𝑥))
30	28, 29	sylibr 224	. . . . . 6 ⊢ ((𝜑 ∧ 𝑥 ⊆ 𝐵 ∧ 𝑦 ⊆ 𝑥) → (𝐹‘𝑦) ⊆ (𝐹‘𝑥))
31		istopclsd.i	. . . . . 6 ⊢ ((𝜑 ∧ 𝑥 ⊆ 𝐵) → (𝐹‘(𝐹‘𝑥)) = (𝐹‘𝑥))
32	7, 2, 17, 30, 31	ismrcd1 37261	. . . . 5 ⊢ (𝜑 → dom (𝐹 ∩ I ) ∈ (Moore‘𝐵))
33		istopclsd.z	. . . . . 6 ⊢ (𝜑 → (𝐹‘∅) = ∅)
34		0elpw 4834	. . . . . . 7 ⊢ ∅ ∈ 𝒫 𝐵
35		fnelfp 6441	. . . . . . 7 ⊢ ((𝐹 Fn 𝒫 𝐵 ∧ ∅ ∈ 𝒫 𝐵) → (∅ ∈ dom (𝐹 ∩ I ) ↔ (𝐹‘∅) = ∅))
36	4, 34, 35	sylancl 694	. . . . . 6 ⊢ (𝜑 → (∅ ∈ dom (𝐹 ∩ I ) ↔ (𝐹‘∅) = ∅))
37	33, 36	mpbird 247	. . . . 5 ⊢ (𝜑 → ∅ ∈ dom (𝐹 ∩ I ))
38		simp1 1061	. . . . . . . 8 ⊢ ((𝜑 ∧ 𝑥 ∈ dom (𝐹 ∩ I ) ∧ 𝑦 ∈ dom (𝐹 ∩ I )) → 𝜑)
39		inss1 3833	. . . . . . . . . . . . 13 ⊢ (𝐹 ∩ I ) ⊆ 𝐹
40		dmss 5323	. . . . . . . . . . . . 13 ⊢ ((𝐹 ∩ I ) ⊆ 𝐹 → dom (𝐹 ∩ I ) ⊆ dom 𝐹)
41	39, 40	ax-mp 5	. . . . . . . . . . . 12 ⊢ dom (𝐹 ∩ I ) ⊆ dom 𝐹
42		fdm 6051	. . . . . . . . . . . . 13 ⊢ (𝐹:𝒫 𝐵⟶𝒫 𝐵 → dom 𝐹 = 𝒫 𝐵)
43	2, 42	syl 17	. . . . . . . . . . . 12 ⊢ (𝜑 → dom 𝐹 = 𝒫 𝐵)
44	41, 43	syl5sseq 3653	. . . . . . . . . . 11 ⊢ (𝜑 → dom (𝐹 ∩ I ) ⊆ 𝒫 𝐵)
45	44	3ad2ant1 1082	. . . . . . . . . 10 ⊢ ((𝜑 ∧ 𝑥 ∈ dom (𝐹 ∩ I ) ∧ 𝑦 ∈ dom (𝐹 ∩ I )) → dom (𝐹 ∩ I ) ⊆ 𝒫 𝐵)
46		simp2 1062	. . . . . . . . . 10 ⊢ ((𝜑 ∧ 𝑥 ∈ dom (𝐹 ∩ I ) ∧ 𝑦 ∈ dom (𝐹 ∩ I )) → 𝑥 ∈ dom (𝐹 ∩ I ))
47	45, 46	sseldd 3604	. . . . . . . . 9 ⊢ ((𝜑 ∧ 𝑥 ∈ dom (𝐹 ∩ I ) ∧ 𝑦 ∈ dom (𝐹 ∩ I )) → 𝑥 ∈ 𝒫 𝐵)
48	47	elpwid 4170	. . . . . . . 8 ⊢ ((𝜑 ∧ 𝑥 ∈ dom (𝐹 ∩ I ) ∧ 𝑦 ∈ dom (𝐹 ∩ I )) → 𝑥 ⊆ 𝐵)
49		simp3 1063	. . . . . . . . . 10 ⊢ ((𝜑 ∧ 𝑥 ∈ dom (𝐹 ∩ I ) ∧ 𝑦 ∈ dom (𝐹 ∩ I )) → 𝑦 ∈ dom (𝐹 ∩ I ))
50	45, 49	sseldd 3604	. . . . . . . . 9 ⊢ ((𝜑 ∧ 𝑥 ∈ dom (𝐹 ∩ I ) ∧ 𝑦 ∈ dom (𝐹 ∩ I )) → 𝑦 ∈ 𝒫 𝐵)
51	50	elpwid 4170	. . . . . . . 8 ⊢ ((𝜑 ∧ 𝑥 ∈ dom (𝐹 ∩ I ) ∧ 𝑦 ∈ dom (𝐹 ∩ I )) → 𝑦 ⊆ 𝐵)
52	38, 48, 51, 22	syl3anc 1326	. . . . . . 7 ⊢ ((𝜑 ∧ 𝑥 ∈ dom (𝐹 ∩ I ) ∧ 𝑦 ∈ dom (𝐹 ∩ I )) → (𝐹‘(𝑥 ∪ 𝑦)) = ((𝐹‘𝑥) ∪ (𝐹‘𝑦)))
53	4	3ad2ant1 1082	. . . . . . . . . 10 ⊢ ((𝜑 ∧ 𝑥 ∈ dom (𝐹 ∩ I ) ∧ 𝑦 ∈ dom (𝐹 ∩ I )) → 𝐹 Fn 𝒫 𝐵)
54		fnelfp 6441	. . . . . . . . . 10 ⊢ ((𝐹 Fn 𝒫 𝐵 ∧ 𝑥 ∈ 𝒫 𝐵) → (𝑥 ∈ dom (𝐹 ∩ I ) ↔ (𝐹‘𝑥) = 𝑥))
55	53, 47, 54	syl2anc 693	. . . . . . . . 9 ⊢ ((𝜑 ∧ 𝑥 ∈ dom (𝐹 ∩ I ) ∧ 𝑦 ∈ dom (𝐹 ∩ I )) → (𝑥 ∈ dom (𝐹 ∩ I ) ↔ (𝐹‘𝑥) = 𝑥))
56	46, 55	mpbid 222	. . . . . . . 8 ⊢ ((𝜑 ∧ 𝑥 ∈ dom (𝐹 ∩ I ) ∧ 𝑦 ∈ dom (𝐹 ∩ I )) → (𝐹‘𝑥) = 𝑥)
57		fnelfp 6441	. . . . . . . . . 10 ⊢ ((𝐹 Fn 𝒫 𝐵 ∧ 𝑦 ∈ 𝒫 𝐵) → (𝑦 ∈ dom (𝐹 ∩ I ) ↔ (𝐹‘𝑦) = 𝑦))
58	53, 50, 57	syl2anc 693	. . . . . . . . 9 ⊢ ((𝜑 ∧ 𝑥 ∈ dom (𝐹 ∩ I ) ∧ 𝑦 ∈ dom (𝐹 ∩ I )) → (𝑦 ∈ dom (𝐹 ∩ I ) ↔ (𝐹‘𝑦) = 𝑦))
59	49, 58	mpbid 222	. . . . . . . 8 ⊢ ((𝜑 ∧ 𝑥 ∈ dom (𝐹 ∩ I ) ∧ 𝑦 ∈ dom (𝐹 ∩ I )) → (𝐹‘𝑦) = 𝑦)
60	56, 59	uneq12d 3768	. . . . . . 7 ⊢ ((𝜑 ∧ 𝑥 ∈ dom (𝐹 ∩ I ) ∧ 𝑦 ∈ dom (𝐹 ∩ I )) → ((𝐹‘𝑥) ∪ (𝐹‘𝑦)) = (𝑥 ∪ 𝑦))
61	52, 60	eqtrd 2656	. . . . . 6 ⊢ ((𝜑 ∧ 𝑥 ∈ dom (𝐹 ∩ I ) ∧ 𝑦 ∈ dom (𝐹 ∩ I )) → (𝐹‘(𝑥 ∪ 𝑦)) = (𝑥 ∪ 𝑦))
62	48, 51	unssd 3789	. . . . . . . 8 ⊢ ((𝜑 ∧ 𝑥 ∈ dom (𝐹 ∩ I ) ∧ 𝑦 ∈ dom (𝐹 ∩ I )) → (𝑥 ∪ 𝑦) ⊆ 𝐵)
63		vex 3203	. . . . . . . . . 10 ⊢ 𝑥 ∈ V
64		vex 3203	. . . . . . . . . 10 ⊢ 𝑦 ∈ V
65	63, 64	unex 6956	. . . . . . . . 9 ⊢ (𝑥 ∪ 𝑦) ∈ V
66	65	elpw 4164	. . . . . . . 8 ⊢ ((𝑥 ∪ 𝑦) ∈ 𝒫 𝐵 ↔ (𝑥 ∪ 𝑦) ⊆ 𝐵)
67	62, 66	sylibr 224	. . . . . . 7 ⊢ ((𝜑 ∧ 𝑥 ∈ dom (𝐹 ∩ I ) ∧ 𝑦 ∈ dom (𝐹 ∩ I )) → (𝑥 ∪ 𝑦) ∈ 𝒫 𝐵)
68		fnelfp 6441	. . . . . . 7 ⊢ ((𝐹 Fn 𝒫 𝐵 ∧ (𝑥 ∪ 𝑦) ∈ 𝒫 𝐵) → ((𝑥 ∪ 𝑦) ∈ dom (𝐹 ∩ I ) ↔ (𝐹‘(𝑥 ∪ 𝑦)) = (𝑥 ∪ 𝑦)))
69	53, 67, 68	syl2anc 693	. . . . . 6 ⊢ ((𝜑 ∧ 𝑥 ∈ dom (𝐹 ∩ I ) ∧ 𝑦 ∈ dom (𝐹 ∩ I )) → ((𝑥 ∪ 𝑦) ∈ dom (𝐹 ∩ I ) ↔ (𝐹‘(𝑥 ∪ 𝑦)) = (𝑥 ∪ 𝑦)))
70	61, 69	mpbird 247	. . . . 5 ⊢ ((𝜑 ∧ 𝑥 ∈ dom (𝐹 ∩ I ) ∧ 𝑦 ∈ dom (𝐹 ∩ I )) → (𝑥 ∪ 𝑦) ∈ dom (𝐹 ∩ I ))
71		eqid 2622	. . . . 5 ⊢ {𝑧 ∈ 𝒫 𝐵 ∣ (𝐵 ∖ 𝑧) ∈ dom (𝐹 ∩ I )} = {𝑧 ∈ 𝒫 𝐵 ∣ (𝐵 ∖ 𝑧) ∈ dom (𝐹 ∩ I )}
72	32, 37, 70, 71	mretopd 20896	. . . 4 ⊢ (𝜑 → ({𝑧 ∈ 𝒫 𝐵 ∣ (𝐵 ∖ 𝑧) ∈ dom (𝐹 ∩ I )} ∈ (TopOn‘𝐵) ∧ dom (𝐹 ∩ I ) = (Clsd‘{𝑧 ∈ 𝒫 𝐵 ∣ (𝐵 ∖ 𝑧) ∈ dom (𝐹 ∩ I )})))
73	72	simpld 475	. . 3 ⊢ (𝜑 → {𝑧 ∈ 𝒫 𝐵 ∣ (𝐵 ∖ 𝑧) ∈ dom (𝐹 ∩ I )} ∈ (TopOn‘𝐵))
74	16, 73	eqeltrd 2701	. 2 ⊢ (𝜑 → 𝐽 ∈ (TopOn‘𝐵))
75		topontop 20718	. . . . . 6 ⊢ (𝐽 ∈ (TopOn‘𝐵) → 𝐽 ∈ Top)
76	74, 75	syl 17	. . . . 5 ⊢ (𝜑 → 𝐽 ∈ Top)
77		eqid 2622	. . . . . 6 ⊢ (mrCls‘(Clsd‘𝐽)) = (mrCls‘(Clsd‘𝐽))
78	77	mrccls 20883	. . . . 5 ⊢ (𝐽 ∈ Top → (cls‘𝐽) = (mrCls‘(Clsd‘𝐽)))
79	76, 78	syl 17	. . . 4 ⊢ (𝜑 → (cls‘𝐽) = (mrCls‘(Clsd‘𝐽)))
80	72	simprd 479	. . . . . 6 ⊢ (𝜑 → dom (𝐹 ∩ I ) = (Clsd‘{𝑧 ∈ 𝒫 𝐵 ∣ (𝐵 ∖ 𝑧) ∈ dom (𝐹 ∩ I )}))
81	16	fveq2d 6195	. . . . . 6 ⊢ (𝜑 → (Clsd‘𝐽) = (Clsd‘{𝑧 ∈ 𝒫 𝐵 ∣ (𝐵 ∖ 𝑧) ∈ dom (𝐹 ∩ I )}))
82	80, 81	eqtr4d 2659	. . . . 5 ⊢ (𝜑 → dom (𝐹 ∩ I ) = (Clsd‘𝐽))
83	82	fveq2d 6195	. . . 4 ⊢ (𝜑 → (mrCls‘dom (𝐹 ∩ I )) = (mrCls‘(Clsd‘𝐽)))
84	79, 83	eqtr4d 2659	. . 3 ⊢ (𝜑 → (cls‘𝐽) = (mrCls‘dom (𝐹 ∩ I )))
85	7, 2, 17, 30, 31	ismrcd2 37262	. . 3 ⊢ (𝜑 → 𝐹 = (mrCls‘dom (𝐹 ∩ I )))
86	84, 85	eqtr4d 2659	. 2 ⊢ (𝜑 → (cls‘𝐽) = 𝐹)
87	74, 86	jca 554	1 ⊢ (𝜑 → (𝐽 ∈ (TopOn‘𝐵) ∧ (cls‘𝐽) = 𝐹))

Syntax hints:   → wi 4   ↔ wb 196   ∧ wa 384   ∧ w3a 1037   = wceq 1483   ∈ wcel 1990  {crab 2916   ∖ cdif 3571   ∪ cun 3572   ∩ cin 3573   ⊆ wss 3574  ∅c0 3915  𝒫 cpw 4158   I cid 5023  dom cdm 5114   Fn wfn 5883  ⟶wf 5884  ‘cfv 5888  mrClscmrc 16243  Topctop 20698  TopOnctopon 20715  Clsdccld 20820  clsccl 20822

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1722  ax-4 1737  ax-5 1839  ax-6 1888  ax-7 1935  ax-8 1992  ax-9 1999  ax-10 2019  ax-11 2034  ax-12 2047  ax-13 2246  ax-ext 2602  ax-rep 4771  ax-sep 4781  ax-nul 4789  ax-pow 4843  ax-pr 4906  ax-un 6949

This theorem depends on definitions:  df-bi 197  df-or 385  df-an 386  df-3an 1039  df-tru 1486  df-ex 1705  df-nf 1710  df-sb 1881  df-eu 2474  df-mo 2475  df-clab 2609  df-cleq 2615  df-clel 2618  df-nfc 2753  df-ne 2795  df-ral 2917  df-rex 2918  df-reu 2919  df-rab 2921  df-v 3202  df-sbc 3436  df-csb 3534  df-dif 3577  df-un 3579  df-in 3581  df-ss 3588  df-nul 3916  df-if 4087  df-pw 4160  df-sn 4178  df-pr 4180  df-op 4184  df-uni 4437  df-int 4476  df-iun 4522  df-iin 4523  df-br 4654  df-opab 4713  df-mpt 4730  df-id 5024  df-xp 5120  df-rel 5121  df-cnv 5122  df-co 5123  df-dm 5124  df-rn 5125  df-res 5126  df-ima 5127  df-iota 5851  df-fun 5890  df-fn 5891  df-f 5892  df-f1 5893  df-fo 5894  df-f1o 5895  df-fv 5896  df-mre 16246  df-mrc 16247  df-top 20699  df-topon 20716  df-cld 20823  df-cls 20825

This theorem is referenced by: (None)