Theorem frgr0 27446

Description: The null graph (graph without vertices) is a friendship graph. (Contributed by AV, 29-Mar-2021.)

Assertion

Ref	Expression
frgr0	⊢ ∅ ∈ FriendGraph

Proof of Theorem frgr0

Dummy variables 𝑘 𝑙 𝑥 are mutually distinct and distinct from all other variables.

Step	Hyp	Ref	Expression
1		usgr0 26358	. 2 ⊢ ∅ ∈ USGraph
2		ral0 4217	. 2 ⊢ ∀𝑘 ∈ ∅ ∀𝑙 ∈ (∅ ∖ {𝑘})∃!𝑥 ∈ ∅ {{𝑥, 𝑘}, {𝑥, 𝑙}} ⊆ (Edg‘∅)
3		vtxval0 26152	. . . 4 ⊢ (Vtx‘∅) = ∅
4	3	eqcomi 2780	. . 3 ⊢ ∅ = (Vtx‘∅)
5		eqid 2771	. . 3 ⊢ (Edg‘∅) = (Edg‘∅)
6	4, 5	frgrusgrfrcond 27441	. 2 ⊢ (∅ ∈ FriendGraph ↔ (∅ ∈ USGraph ∧ ∀𝑘 ∈ ∅ ∀𝑙 ∈ (∅ ∖ {𝑘})∃!𝑥 ∈ ∅ {{𝑥, 𝑘}, {𝑥, 𝑙}} ⊆ (Edg‘∅)))
7	1, 2, 6	mpbir2an 690	1 ⊢ ∅ ∈ FriendGraph

Syntax hints:   ∈ wcel 2145  ∀wral 3061  ∃!wreu 3063   ∖ cdif 3720   ⊆ wss 3723  ∅c0 4063  {csn 4316  {cpr 4318  ‘cfv 6031  Vtxcvtx 26095  Edgcedg 26160  USGraphcusgr 26266   FriendGraph cfrgr 27438

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1870  ax-4 1885  ax-5 1991  ax-6 2057  ax-7 2093  ax-8 2147  ax-9 2154  ax-10 2174  ax-11 2190  ax-12 2203  ax-13 2408  ax-ext 2751  ax-sep 4915  ax-nul 4923  ax-pow 4974  ax-pr 5034

This theorem depends on definitions:  df-bi 197  df-an 383  df-or 837  df-3an 1073  df-tru 1634  df-ex 1853  df-nf 1858  df-sb 2050  df-eu 2622  df-mo 2623  df-clab 2758  df-cleq 2764  df-clel 2767  df-nfc 2902  df-ne 2944  df-ral 3066  df-rex 3067  df-reu 3068  df-rab 3070  df-v 3353  df-sbc 3588  df-dif 3726  df-un 3728  df-in 3730  df-ss 3737  df-nul 4064  df-if 4226  df-pw 4299  df-sn 4317  df-pr 4319  df-op 4323  df-uni 4575  df-br 4787  df-opab 4847  df-mpt 4864  df-id 5157  df-xp 5255  df-rel 5256  df-cnv 5257  df-co 5258  df-dm 5259  df-rn 5260  df-iota 5994  df-fun 6033  df-fn 6034  df-f 6035  df-f1 6036  df-fv 6039  df-slot 16068  df-base 16070  df-edgf 26089  df-vtx 26097  df-iedg 26098  df-usgr 26268  df-frgr 27439

This theorem is referenced by: (None)