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Mirrors > Home > MPE Home > Th. List > nfeu1ALT | Structured version Visualization version GIF version |
Description: Alternate proof of nfeu1 2670. This illustrates the systematic way of proving nonfreeness in a defined expression: consider the definiens as a tree whose nodes are its subformulas, and prove by tree-induction nonfreeness of each node, starting from the leaves (generally using nfv 1911 or nf* theorems for previously defined expressions) and up to the root. Here, the definiens is a conjunction of two previously defined expressions, which automatically yields the present proof. (Contributed by BJ, 2-Oct-2022.) (Proof modification is discouraged.) (New usage is discouraged.) |
Ref | Expression |
---|---|
nfeu1ALT | ⊢ Ⅎ𝑥∃!𝑥𝜑 |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | df-eu 2650 | . 2 ⊢ (∃!𝑥𝜑 ↔ (∃𝑥𝜑 ∧ ∃*𝑥𝜑)) | |
2 | nfe1 2150 | . . 3 ⊢ Ⅎ𝑥∃𝑥𝜑 | |
3 | nfmo1 2637 | . . 3 ⊢ Ⅎ𝑥∃*𝑥𝜑 | |
4 | 2, 3 | nfan 1896 | . 2 ⊢ Ⅎ𝑥(∃𝑥𝜑 ∧ ∃*𝑥𝜑) |
5 | 1, 4 | nfxfr 1849 | 1 ⊢ Ⅎ𝑥∃!𝑥𝜑 |
Colors of variables: wff setvar class |
Syntax hints: ∧ wa 398 ∃wex 1776 Ⅎwnf 1780 ∃*wmo 2616 ∃!weu 2649 |
This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-3 8 ax-gen 1792 ax-4 1806 ax-5 1907 ax-6 1966 ax-7 2011 ax-10 2141 ax-11 2156 ax-12 2172 |
This theorem depends on definitions: df-bi 209 df-an 399 df-or 844 df-tru 1536 df-ex 1777 df-nf 1781 df-mo 2618 df-eu 2650 |
This theorem is referenced by: (None) |
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