Definition df-xr 8118

Description: Define the set of extended reals that includes plus and minus infinity. Definition 12-3.1 of [Gleason] p. 173. (Contributed by NM, 13-Oct-2005.)

Assertion

Ref	Expression
df-xr	⊢ ℝ* = (ℝ ∪ {+∞, -∞})

Detailed syntax breakdown of Definition df-xr

Step	Hyp	Ref	Expression
1		cxr 8113	. 2 class ℝ*
2		cr 7931	. . 3 class ℝ
3		cpnf 8111	. . . 4 class +∞
4		cmnf 8112	. . . 4 class -∞
5	3, 4	cpr 3635	. . 3 class {+∞, -∞}
6	2, 5	cun 3165	. 2 class (ℝ ∪ {+∞, -∞})
7	1, 6	wceq 1373	1 wff ℝ* = (ℝ ∪ {+∞, -∞})

This definition is referenced by:  ressxr  8123  pnfxr  8132  mnfxr  8136  ltrelxr  8140  elxr  9905  xrex  9985