Theorem df3o3 43338

Description: Ordinal 3, fully expanded. (Contributed by RP, 8-Jul-2021.)

Assertion

Ref	Expression
df3o3	⊢ 3o = {∅, {∅}, {∅, {∅}}}

Proof of Theorem df3o3

Step	Hyp	Ref	Expression
1		df-3o 8482	. 2 ⊢ 3o = suc 2o
2		df2o2 8489	. . . 4 ⊢ 2o = {∅, {∅}}
3	2	sneqi 4612	. . . 4 ⊢ {2o} = {{∅, {∅}}}
4	2, 3	uneq12i 4141	. . 3 ⊢ (2o ∪ {2o}) = ({∅, {∅}} ∪ {{∅, {∅}}})
5		df-suc 6358	. . 3 ⊢ suc 2o = (2o ∪ {2o})
6		df-tp 4606	. . 3 ⊢ {∅, {∅}, {∅, {∅}}} = ({∅, {∅}} ∪ {{∅, {∅}}})
7	4, 5, 6	3eqtr4i 2768	. 2 ⊢ suc 2o = {∅, {∅}, {∅, {∅}}}
8	1, 7	eqtri 2758	1 ⊢ 3o = {∅, {∅}, {∅, {∅}}}

Syntax hints:   = wceq 1540   ∪ cun 3924  ∅c0 4308  {csn 4601  {cpr 4603  {ctp 4605  suc csuc 6354  2_oc2o 8474  3_oc3o 8475

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1795  ax-4 1809  ax-5 1910  ax-6 1967  ax-7 2007  ax-8 2110  ax-9 2118  ax-ext 2707

This theorem depends on definitions:  df-bi 207  df-an 396  df-or 848  df-tru 1543  df-fal 1553  df-ex 1780  df-sb 2065  df-clab 2714  df-cleq 2727  df-clel 2809  df-v 3461  df-dif 3929  df-un 3931  df-nul 4309  df-sn 4602  df-pr 4604  df-tp 4606  df-suc 6358  df-1o 8480  df-2o 8481  df-3o 8482

This theorem is referenced by: (None)