This is an inofficial mirror of http://metamath.tirix.org for personal testing of a visualizer extension only.
Description: An alternate definition of df-inito using universal property. See also the "Equivalent formulations" section of https://en.wikipedia.org/wiki/Initial_and_terminal_objects . (Contributed by Zhi Wang, 23-Oct-2025)
| Ref | Expression | ||
|---|---|---|---|
| Assertion | dfinito4 | ⊢ InitO = ( 𝑐 ∈ Cat ↦ ⦋ ( SetCat ‘ 1o ) / 𝑑 ⦌ ⦋ ( ( 1st ‘ ( 𝑑 Δfunc 𝑐 ) ) ‘ ∅ ) / 𝑓 ⦌ dom ( 𝑓 ( 𝑐 UP 𝑑 ) ∅ ) ) |
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 1 | initofn | ⊢ InitO Fn Cat | |
| 2 | ovex | ⊢ ( 𝑓 ( 𝑐 UP 𝑑 ) ∅ ) ∈ V | |
| 3 | 2 | dmex | ⊢ dom ( 𝑓 ( 𝑐 UP 𝑑 ) ∅ ) ∈ V |
| 4 | 3 | csbex | ⊢ ⦋ ( ( 1st ‘ ( 𝑑 Δfunc 𝑐 ) ) ‘ ∅ ) / 𝑓 ⦌ dom ( 𝑓 ( 𝑐 UP 𝑑 ) ∅ ) ∈ V |
| 5 | 4 | csbex | ⊢ ⦋ ( SetCat ‘ 1o ) / 𝑑 ⦌ ⦋ ( ( 1st ‘ ( 𝑑 Δfunc 𝑐 ) ) ‘ ∅ ) / 𝑓 ⦌ dom ( 𝑓 ( 𝑐 UP 𝑑 ) ∅ ) ∈ V |
| 6 | eqid | ⊢ ( 𝑐 ∈ Cat ↦ ⦋ ( SetCat ‘ 1o ) / 𝑑 ⦌ ⦋ ( ( 1st ‘ ( 𝑑 Δfunc 𝑐 ) ) ‘ ∅ ) / 𝑓 ⦌ dom ( 𝑓 ( 𝑐 UP 𝑑 ) ∅ ) ) = ( 𝑐 ∈ Cat ↦ ⦋ ( SetCat ‘ 1o ) / 𝑑 ⦌ ⦋ ( ( 1st ‘ ( 𝑑 Δfunc 𝑐 ) ) ‘ ∅ ) / 𝑓 ⦌ dom ( 𝑓 ( 𝑐 UP 𝑑 ) ∅ ) ) | |
| 7 | 5 6 | fnmpti | ⊢ ( 𝑐 ∈ Cat ↦ ⦋ ( SetCat ‘ 1o ) / 𝑑 ⦌ ⦋ ( ( 1st ‘ ( 𝑑 Δfunc 𝑐 ) ) ‘ ∅ ) / 𝑓 ⦌ dom ( 𝑓 ( 𝑐 UP 𝑑 ) ∅ ) ) Fn Cat |
| 8 | eqfnfv | ⊢ ( ( InitO Fn Cat ∧ ( 𝑐 ∈ Cat ↦ ⦋ ( SetCat ‘ 1o ) / 𝑑 ⦌ ⦋ ( ( 1st ‘ ( 𝑑 Δfunc 𝑐 ) ) ‘ ∅ ) / 𝑓 ⦌ dom ( 𝑓 ( 𝑐 UP 𝑑 ) ∅ ) ) Fn Cat ) → ( InitO = ( 𝑐 ∈ Cat ↦ ⦋ ( SetCat ‘ 1o ) / 𝑑 ⦌ ⦋ ( ( 1st ‘ ( 𝑑 Δfunc 𝑐 ) ) ‘ ∅ ) / 𝑓 ⦌ dom ( 𝑓 ( 𝑐 UP 𝑑 ) ∅ ) ) ↔ ∀ 𝑒 ∈ Cat ( InitO ‘ 𝑒 ) = ( ( 𝑐 ∈ Cat ↦ ⦋ ( SetCat ‘ 1o ) / 𝑑 ⦌ ⦋ ( ( 1st ‘ ( 𝑑 Δfunc 𝑐 ) ) ‘ ∅ ) / 𝑓 ⦌ dom ( 𝑓 ( 𝑐 UP 𝑑 ) ∅ ) ) ‘ 𝑒 ) ) ) | |
| 9 | 1 7 8 | mp2an | ⊢ ( InitO = ( 𝑐 ∈ Cat ↦ ⦋ ( SetCat ‘ 1o ) / 𝑑 ⦌ ⦋ ( ( 1st ‘ ( 𝑑 Δfunc 𝑐 ) ) ‘ ∅ ) / 𝑓 ⦌ dom ( 𝑓 ( 𝑐 UP 𝑑 ) ∅ ) ) ↔ ∀ 𝑒 ∈ Cat ( InitO ‘ 𝑒 ) = ( ( 𝑐 ∈ Cat ↦ ⦋ ( SetCat ‘ 1o ) / 𝑑 ⦌ ⦋ ( ( 1st ‘ ( 𝑑 Δfunc 𝑐 ) ) ‘ ∅ ) / 𝑓 ⦌ dom ( 𝑓 ( 𝑐 UP 𝑑 ) ∅ ) ) ‘ 𝑒 ) ) |
| 10 | eqid | ⊢ ( SetCat ‘ 1o ) = ( SetCat ‘ 1o ) | |
| 11 | eqid | ⊢ ( ( 1st ‘ ( ( SetCat ‘ 1o ) Δfunc 𝑒 ) ) ‘ ∅ ) = ( ( 1st ‘ ( ( SetCat ‘ 1o ) Δfunc 𝑒 ) ) ‘ ∅ ) | |
| 12 | 10 11 | isinito3 | ⊢ ( 𝑥 ∈ ( InitO ‘ 𝑒 ) ↔ 𝑥 ∈ dom ( ( ( 1st ‘ ( ( SetCat ‘ 1o ) Δfunc 𝑒 ) ) ‘ ∅ ) ( 𝑒 UP ( SetCat ‘ 1o ) ) ∅ ) ) |
| 13 | 12 | eqriv | ⊢ ( InitO ‘ 𝑒 ) = dom ( ( ( 1st ‘ ( ( SetCat ‘ 1o ) Δfunc 𝑒 ) ) ‘ ∅ ) ( 𝑒 UP ( SetCat ‘ 1o ) ) ∅ ) |
| 14 | fvex | ⊢ ( SetCat ‘ 1o ) ∈ V | |
| 15 | fvexd | ⊢ ( 𝑑 = ( SetCat ‘ 1o ) → ( ( 1st ‘ ( 𝑑 Δfunc 𝑒 ) ) ‘ ∅ ) ∈ V ) | |
| 16 | simpl | ⊢ ( ( 𝑑 = ( SetCat ‘ 1o ) ∧ 𝑓 = ( ( 1st ‘ ( 𝑑 Δfunc 𝑒 ) ) ‘ ∅ ) ) → 𝑑 = ( SetCat ‘ 1o ) ) | |
| 17 | 16 | oveq2d | ⊢ ( ( 𝑑 = ( SetCat ‘ 1o ) ∧ 𝑓 = ( ( 1st ‘ ( 𝑑 Δfunc 𝑒 ) ) ‘ ∅ ) ) → ( 𝑒 UP 𝑑 ) = ( 𝑒 UP ( SetCat ‘ 1o ) ) ) |
| 18 | simpr | ⊢ ( ( 𝑑 = ( SetCat ‘ 1o ) ∧ 𝑓 = ( ( 1st ‘ ( 𝑑 Δfunc 𝑒 ) ) ‘ ∅ ) ) → 𝑓 = ( ( 1st ‘ ( 𝑑 Δfunc 𝑒 ) ) ‘ ∅ ) ) | |
| 19 | 16 | fvoveq1d | ⊢ ( ( 𝑑 = ( SetCat ‘ 1o ) ∧ 𝑓 = ( ( 1st ‘ ( 𝑑 Δfunc 𝑒 ) ) ‘ ∅ ) ) → ( 1st ‘ ( 𝑑 Δfunc 𝑒 ) ) = ( 1st ‘ ( ( SetCat ‘ 1o ) Δfunc 𝑒 ) ) ) |
| 20 | 19 | fveq1d | ⊢ ( ( 𝑑 = ( SetCat ‘ 1o ) ∧ 𝑓 = ( ( 1st ‘ ( 𝑑 Δfunc 𝑒 ) ) ‘ ∅ ) ) → ( ( 1st ‘ ( 𝑑 Δfunc 𝑒 ) ) ‘ ∅ ) = ( ( 1st ‘ ( ( SetCat ‘ 1o ) Δfunc 𝑒 ) ) ‘ ∅ ) ) |
| 21 | 18 20 | eqtrd | ⊢ ( ( 𝑑 = ( SetCat ‘ 1o ) ∧ 𝑓 = ( ( 1st ‘ ( 𝑑 Δfunc 𝑒 ) ) ‘ ∅ ) ) → 𝑓 = ( ( 1st ‘ ( ( SetCat ‘ 1o ) Δfunc 𝑒 ) ) ‘ ∅ ) ) |
| 22 | eqidd | ⊢ ( ( 𝑑 = ( SetCat ‘ 1o ) ∧ 𝑓 = ( ( 1st ‘ ( 𝑑 Δfunc 𝑒 ) ) ‘ ∅ ) ) → ∅ = ∅ ) | |
| 23 | 17 21 22 | oveq123d | ⊢ ( ( 𝑑 = ( SetCat ‘ 1o ) ∧ 𝑓 = ( ( 1st ‘ ( 𝑑 Δfunc 𝑒 ) ) ‘ ∅ ) ) → ( 𝑓 ( 𝑒 UP 𝑑 ) ∅ ) = ( ( ( 1st ‘ ( ( SetCat ‘ 1o ) Δfunc 𝑒 ) ) ‘ ∅ ) ( 𝑒 UP ( SetCat ‘ 1o ) ) ∅ ) ) |
| 24 | 23 | dmeqd | ⊢ ( ( 𝑑 = ( SetCat ‘ 1o ) ∧ 𝑓 = ( ( 1st ‘ ( 𝑑 Δfunc 𝑒 ) ) ‘ ∅ ) ) → dom ( 𝑓 ( 𝑒 UP 𝑑 ) ∅ ) = dom ( ( ( 1st ‘ ( ( SetCat ‘ 1o ) Δfunc 𝑒 ) ) ‘ ∅ ) ( 𝑒 UP ( SetCat ‘ 1o ) ) ∅ ) ) |
| 25 | 15 24 | csbied | ⊢ ( 𝑑 = ( SetCat ‘ 1o ) → ⦋ ( ( 1st ‘ ( 𝑑 Δfunc 𝑒 ) ) ‘ ∅ ) / 𝑓 ⦌ dom ( 𝑓 ( 𝑒 UP 𝑑 ) ∅ ) = dom ( ( ( 1st ‘ ( ( SetCat ‘ 1o ) Δfunc 𝑒 ) ) ‘ ∅ ) ( 𝑒 UP ( SetCat ‘ 1o ) ) ∅ ) ) |
| 26 | 14 25 | csbie | ⊢ ⦋ ( SetCat ‘ 1o ) / 𝑑 ⦌ ⦋ ( ( 1st ‘ ( 𝑑 Δfunc 𝑒 ) ) ‘ ∅ ) / 𝑓 ⦌ dom ( 𝑓 ( 𝑒 UP 𝑑 ) ∅ ) = dom ( ( ( 1st ‘ ( ( SetCat ‘ 1o ) Δfunc 𝑒 ) ) ‘ ∅ ) ( 𝑒 UP ( SetCat ‘ 1o ) ) ∅ ) |
| 27 | 13 26 | eqtr4i | ⊢ ( InitO ‘ 𝑒 ) = ⦋ ( SetCat ‘ 1o ) / 𝑑 ⦌ ⦋ ( ( 1st ‘ ( 𝑑 Δfunc 𝑒 ) ) ‘ ∅ ) / 𝑓 ⦌ dom ( 𝑓 ( 𝑒 UP 𝑑 ) ∅ ) |
| 28 | oveq2 | ⊢ ( 𝑐 = 𝑒 → ( 𝑑 Δfunc 𝑐 ) = ( 𝑑 Δfunc 𝑒 ) ) | |
| 29 | 28 | fveq2d | ⊢ ( 𝑐 = 𝑒 → ( 1st ‘ ( 𝑑 Δfunc 𝑐 ) ) = ( 1st ‘ ( 𝑑 Δfunc 𝑒 ) ) ) |
| 30 | 29 | fveq1d | ⊢ ( 𝑐 = 𝑒 → ( ( 1st ‘ ( 𝑑 Δfunc 𝑐 ) ) ‘ ∅ ) = ( ( 1st ‘ ( 𝑑 Δfunc 𝑒 ) ) ‘ ∅ ) ) |
| 31 | oveq1 | ⊢ ( 𝑐 = 𝑒 → ( 𝑐 UP 𝑑 ) = ( 𝑒 UP 𝑑 ) ) | |
| 32 | 31 | oveqd | ⊢ ( 𝑐 = 𝑒 → ( 𝑓 ( 𝑐 UP 𝑑 ) ∅ ) = ( 𝑓 ( 𝑒 UP 𝑑 ) ∅ ) ) |
| 33 | 32 | dmeqd | ⊢ ( 𝑐 = 𝑒 → dom ( 𝑓 ( 𝑐 UP 𝑑 ) ∅ ) = dom ( 𝑓 ( 𝑒 UP 𝑑 ) ∅ ) ) |
| 34 | 30 33 | csbeq12dv | ⊢ ( 𝑐 = 𝑒 → ⦋ ( ( 1st ‘ ( 𝑑 Δfunc 𝑐 ) ) ‘ ∅ ) / 𝑓 ⦌ dom ( 𝑓 ( 𝑐 UP 𝑑 ) ∅ ) = ⦋ ( ( 1st ‘ ( 𝑑 Δfunc 𝑒 ) ) ‘ ∅ ) / 𝑓 ⦌ dom ( 𝑓 ( 𝑒 UP 𝑑 ) ∅ ) ) |
| 35 | 34 | csbeq2dv | ⊢ ( 𝑐 = 𝑒 → ⦋ ( SetCat ‘ 1o ) / 𝑑 ⦌ ⦋ ( ( 1st ‘ ( 𝑑 Δfunc 𝑐 ) ) ‘ ∅ ) / 𝑓 ⦌ dom ( 𝑓 ( 𝑐 UP 𝑑 ) ∅ ) = ⦋ ( SetCat ‘ 1o ) / 𝑑 ⦌ ⦋ ( ( 1st ‘ ( 𝑑 Δfunc 𝑒 ) ) ‘ ∅ ) / 𝑓 ⦌ dom ( 𝑓 ( 𝑒 UP 𝑑 ) ∅ ) ) |
| 36 | ovex | ⊢ ( 𝑓 ( 𝑒 UP 𝑑 ) ∅ ) ∈ V | |
| 37 | 36 | dmex | ⊢ dom ( 𝑓 ( 𝑒 UP 𝑑 ) ∅ ) ∈ V |
| 38 | 37 | csbex | ⊢ ⦋ ( ( 1st ‘ ( 𝑑 Δfunc 𝑒 ) ) ‘ ∅ ) / 𝑓 ⦌ dom ( 𝑓 ( 𝑒 UP 𝑑 ) ∅ ) ∈ V |
| 39 | 38 | csbex | ⊢ ⦋ ( SetCat ‘ 1o ) / 𝑑 ⦌ ⦋ ( ( 1st ‘ ( 𝑑 Δfunc 𝑒 ) ) ‘ ∅ ) / 𝑓 ⦌ dom ( 𝑓 ( 𝑒 UP 𝑑 ) ∅ ) ∈ V |
| 40 | 35 6 39 | fvmpt | ⊢ ( 𝑒 ∈ Cat → ( ( 𝑐 ∈ Cat ↦ ⦋ ( SetCat ‘ 1o ) / 𝑑 ⦌ ⦋ ( ( 1st ‘ ( 𝑑 Δfunc 𝑐 ) ) ‘ ∅ ) / 𝑓 ⦌ dom ( 𝑓 ( 𝑐 UP 𝑑 ) ∅ ) ) ‘ 𝑒 ) = ⦋ ( SetCat ‘ 1o ) / 𝑑 ⦌ ⦋ ( ( 1st ‘ ( 𝑑 Δfunc 𝑒 ) ) ‘ ∅ ) / 𝑓 ⦌ dom ( 𝑓 ( 𝑒 UP 𝑑 ) ∅ ) ) |
| 41 | 27 40 | eqtr4id | ⊢ ( 𝑒 ∈ Cat → ( InitO ‘ 𝑒 ) = ( ( 𝑐 ∈ Cat ↦ ⦋ ( SetCat ‘ 1o ) / 𝑑 ⦌ ⦋ ( ( 1st ‘ ( 𝑑 Δfunc 𝑐 ) ) ‘ ∅ ) / 𝑓 ⦌ dom ( 𝑓 ( 𝑐 UP 𝑑 ) ∅ ) ) ‘ 𝑒 ) ) |
| 42 | 9 41 | mprgbir | ⊢ InitO = ( 𝑐 ∈ Cat ↦ ⦋ ( SetCat ‘ 1o ) / 𝑑 ⦌ ⦋ ( ( 1st ‘ ( 𝑑 Δfunc 𝑐 ) ) ‘ ∅ ) / 𝑓 ⦌ dom ( 𝑓 ( 𝑐 UP 𝑑 ) ∅ ) ) |