Definition df-mnf 11248

Description: Define minus infinity as the power set of plus infinity. Note that the definition is arbitrary, requiring only that -∞ be a set not in ℝ and different from +∞ (see mnfnre 11254 and pnfnemnf 11266). (Contributed by NM, 13-Oct-2005.) (New usage is discouraged.)

Assertion

Ref	Expression
df-mnf	⊢ -∞ = 𝒫 +∞

Detailed syntax breakdown of Definition df-mnf

Step	Hyp	Ref	Expression
1		cmnf 11243	. 2 class -∞
2		cpnf 11242	. . 3 class +∞
3	2	cpw 4602	. 2 class 𝒫 +∞
4	1, 3	wceq 1542	1 wff -∞ = 𝒫 +∞

This definition is referenced by:  mnfnre  11254  pnfnemnf  11266  mnfxr  11268