Theorem xnegpnf 10124

Description: Minus +oo. Remark of [BourbakiTop1] p. IV.15. (Contributed by FL, 26-Dec-2011.)

Assertion

Ref	Expression
xnegpnf	|- -e +oo = -oo

Proof of Theorem xnegpnf

Step	Hyp	Ref	Expression
1		df-xneg 10068	. 2 |- -e +oo = if ( +oo = +oo , -oo , if ( +oo = -oo , +oo , -u +oo ) )
2		eqid 2231	. . 3 |- +oo = +oo
3	2	iftruei 3615	. 2 |- if ( +oo = +oo , -oo , if ( +oo = -oo , +oo , -u +oo ) ) = -oo
4	1, 3	eqtri 2252	1 |- -e +oo = -oo

Syntax hints:   = wceq 1398   ifcif 3607   +oocpnf 8270   -oocmnf 8271   -ucneg 8410   -ecxne 10065

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 106  ax-ia2 107  ax-ia3 108  ax-in2 620  ax-io 717  ax-5 1496  ax-7 1497  ax-gen 1498  ax-ie1 1542  ax-ie2 1543  ax-8 1553  ax-11 1555  ax-4 1559  ax-17 1575  ax-i9 1579  ax-ial 1583  ax-i5r 1584  ax-ext 2213

This theorem depends on definitions:  df-bi 117  df-nf 1510  df-sb 1811  df-clab 2218  df-cleq 2224  df-clel 2227  df-if 3608  df-xneg 10068

This theorem is referenced by:  xnegcl  10128  xnegneg  10129  xltnegi  10131  xnegid  10155  xnegdi  10164  xaddass2  10166  xsubge0  10177  xposdif  10178  xlesubadd  10179  xblss2ps  15215  xblss2  15216