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Definition df-xr 8871
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  |-  RR*  =  ( RR  u.  {  +oo , 
-oo } )

Detailed syntax breakdown of Definition df-xr
StepHypRef Expression
1 cxr 8866 . 2  class  RR*
2 cr 8736 . . 3  class  RR
3 cpnf 8864 . . . 4  class  +oo
4 cmnf 8865 . . . 4  class  -oo
53, 4cpr 3641 . . 3  class  {  +oo , 
-oo }
62, 5cun 3150 . 2  class  ( RR  u.  {  +oo ,  -oo } )
71, 6wceq 1623 1  wff  RR*  =  ( RR  u.  {  +oo , 
-oo } )
Colors of variables: wff set class
This definition is referenced by:  ressxr  8876  ltrelxr  8886  ssxr  8892  xrex  10351  pnfxr  10455  mnfxr  10456  elxr  10458
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