Theorem ringen1zr

Description: The only unital ring with one element is the zero ring (at least if its operations are internal binary operations). Note: The assumption R e. Ring could be weakened if a definition of a non-unital ring ("Rng") was available (it would be sufficient that the multiplication is closed). (Contributed by FL, 15-Feb-2010) (Revised by AV, 25-Jan-2020)

	Ref	Expression
Hypotheses	ring1zr.b	$$⊢B={\mathrm{Base}}_R$$
	ring1zr.p	$$⊢\underset{\dot{}}{+}={+}_R$$
	ring1zr.t	$$⊢\underset{\dot{}}{\ast }={\cdot }_R$$
	ringen1zr.0	$$⊢Z=0_R$$
Assertion	ringen1zr	$$⊢\left(R\in \mathrm{Ring}\wedge \underset{\dot{}}{+}Fn\left(B\times B\right)\wedge \underset{\dot{}}{\ast }Fn\left(B\times B\right)\right)\to \left(B\approx 1_{𝑜}\leftrightarrow \left(\underset{\dot{}}{+}=\left\{⟨⟨Z,Z⟩,Z⟩\right\}\wedge \underset{\dot{}}{\ast }=\left\{⟨⟨Z,Z⟩,Z⟩\right\}\right)\right)$$

Proof

Step	Hyp	Ref	Expression
1		ring1zr.b	$$⊢B={\mathrm{Base}}_R$$
2		ring1zr.p	$$⊢\underset{\dot{}}{+}={+}_R$$
3		ring1zr.t	$$⊢\underset{\dot{}}{\ast }={\cdot }_R$$
4		ringen1zr.0	$$⊢Z=0_R$$
5	1 4	ring0cl	$$⊢R\in \mathrm{Ring}\to Z\in B$$
6	5	3ad2ant1	$$⊢\left(R\in \mathrm{Ring}\wedge \underset{\dot{}}{+}Fn\left(B\times B\right)\wedge \underset{\dot{}}{\ast }Fn\left(B\times B\right)\right)\to Z\in B$$
7	1 2 3	rngen1zr	$$⊢\left(\left(R\in \mathrm{Ring}\wedge \underset{\dot{}}{+}Fn\left(B\times B\right)\wedge \underset{\dot{}}{\ast }Fn\left(B\times B\right)\right)\wedge Z\in B\right)\to \left(B\approx 1_{𝑜}\leftrightarrow \left(\underset{\dot{}}{+}=\left\{⟨⟨Z,Z⟩,Z⟩\right\}\wedge \underset{\dot{}}{\ast }=\left\{⟨⟨Z,Z⟩,Z⟩\right\}\right)\right)$$
8	6 7	mpdan	$$⊢\left(R\in \mathrm{Ring}\wedge \underset{\dot{}}{+}Fn\left(B\times B\right)\wedge \underset{\dot{}}{\ast }Fn\left(B\times B\right)\right)\to \left(B\approx 1_{𝑜}\leftrightarrow \left(\underset{\dot{}}{+}=\left\{⟨⟨Z,Z⟩,Z⟩\right\}\wedge \underset{\dot{}}{\ast }=\left\{⟨⟨Z,Z⟩,Z⟩\right\}\right)\right)$$