Theorem repiecef 16799

Description: Piecewise definition on the reals yields a function. The function agrees with F and G on their respective parts of the real line; see repiecele0 16797 and repiecege0 16798. From an online post by James E Hanson. The construction was published in Martín Hötzel Escardó, "Effective and sequential definition by cases on the reals via infinite signed-digit numerals", Electronic Notes in Theoretical Computer Science 10 (1998), page 2, https://martinescardo.github.io/papers/lexnew.pdf. 16798 (Contributed by Jim Kingdon, 27-Apr-2026.)

Hypotheses

Ref	Expression
repiece.f	|- ( ph -> F : ( -oo (,] 0 ) --> RR )
repiece.g	|- ( ph -> G : ( 0 [,) +oo ) --> RR )
repiece.0	|- ( ph -> ( F ` 0 ) = ( G ` 0 ) )
repiece.h	|- H = ( x e. RR |-> ( ( ( F ` inf ( { x , 0 } , RR , < ) ) + ( G ` sup ( { x , 0 } , RR , < ) ) ) - ( F ` 0 ) ) )

Assertion

Ref	Expression
repiecef	|- ( ph -> H : RR --> RR )

Distinct variable groups:   x, F   x, G

Allowed substitution hints:   ph( x)   H( x)

Proof of Theorem repiecef

Dummy variable y is distinct from all other variables.

Step	Hyp	Ref	Expression
1		repiece.f	. . . . 5 |- ( ph -> F : ( -oo (,] 0 ) --> RR )
2		repiece.g	. . . . 5 |- ( ph -> G : ( 0 [,) +oo ) --> RR )
3		repiece.0	. . . . 5 |- ( ph -> ( F ` 0 ) = ( G ` 0 ) )
4		repiece.h	. . . . 5 |- H = ( x e. RR |-> ( ( ( F ` inf ( { x , 0 } , RR , < ) ) + ( G ` sup ( { x , 0 } , RR , < ) ) ) - ( F ` 0 ) ) )
5	1, 2, 3, 4	repiecelem 16796	. . . 4 |- ( ( ph /\ y e. RR ) -> ( ( ( F ` inf ( { y , 0 } , RR , < ) ) + ( G ` sup ( { y , 0 } , RR , < ) ) ) - ( F ` 0 ) ) e. RR )
6	5	ralrimiva 2615	. . 3 |- ( ph -> A. y e. RR ( ( ( F ` inf ( { y , 0 } , RR , < ) ) + ( G ` sup ( { y , 0 } , RR , < ) ) ) - ( F ` 0 ) ) e. RR )
7		preq1 3767	. . . . . . . . 9 |- ( y = x -> { y , 0 } = { x , 0 } )
8	7	infeq1d 7302	. . . . . . . 8 |- ( y = x -> inf ( { y , 0 } , RR , < ) = inf ( { x , 0 } , RR , < ) )
9	8	fveq2d 5673	. . . . . . 7 |- ( y = x -> ( F ` inf ( { y , 0 } , RR , < ) ) = ( F ` inf ( { x , 0 } , RR , < ) ) )
10	7	supeq1d 7277	. . . . . . . 8 |- ( y = x -> sup ( { y , 0 } , RR , < ) = sup ( { x , 0 } , RR , < ) )
11	10	fveq2d 5673	. . . . . . 7 |- ( y = x -> ( G ` sup ( { y , 0 } , RR , < ) ) = ( G ` sup ( { x , 0 } , RR , < ) ) )
12	9, 11	oveq12d 6067	. . . . . 6 |- ( y = x -> ( ( F ` inf ( { y , 0 } , RR , < ) ) + ( G ` sup ( { y , 0 } , RR , < ) ) ) = ( ( F ` inf ( { x , 0 } , RR , < ) ) + ( G ` sup ( { x , 0 } , RR , < ) ) ) )
13	12	oveq1d 6064	. . . . 5 |- ( y = x -> ( ( ( F ` inf ( { y , 0 } , RR , < ) ) + ( G ` sup ( { y , 0 } , RR , < ) ) ) - ( F ` 0 ) ) = ( ( ( F ` inf ( { x , 0 } , RR , < ) ) + ( G ` sup ( { x , 0 } , RR , < ) ) ) - ( F ` 0 ) ) )
14	13	eleq1d 2301	. . . 4 |- ( y = x -> ( ( ( ( F ` inf ( { y , 0 } , RR , < ) ) + ( G ` sup ( { y , 0 } , RR , < ) ) ) - ( F ` 0 ) ) e. RR <-> ( ( ( F ` inf ( { x , 0 } , RR , < ) ) + ( G ` sup ( { x , 0 } , RR , < ) ) ) - ( F ` 0 ) ) e. RR ) )
15	14	cbvralv 2777	. . 3 |- ( A. y e. RR ( ( ( F ` inf ( { y , 0 } , RR , < ) ) + ( G ` sup ( { y , 0 } , RR , < ) ) ) - ( F ` 0 ) ) e. RR <-> A. x e. RR ( ( ( F ` inf ( { x , 0 } , RR , < ) ) + ( G ` sup ( { x , 0 } , RR , < ) ) ) - ( F ` 0 ) ) e. RR )
16	6, 15	sylib 122	. 2 |- ( ph -> A. x e. RR ( ( ( F ` inf ( { x , 0 } , RR , < ) ) + ( G ` sup ( { x , 0 } , RR , < ) ) ) - ( F ` 0 ) ) e. RR )
17	4	fmpt 5826	. 2 |- ( A. x e. RR ( ( ( F ` inf ( { x , 0 } , RR , < ) ) + ( G ` sup ( { x , 0 } , RR , < ) ) ) - ( F ` 0 ) ) e. RR <-> H : RR --> RR )
18	16, 17	sylib 122	1 |- ( ph -> H : RR --> RR )

Syntax hints:   -> wi 4   = wceq 1398   e. wcel 2203   A.wral 2520   {cpr 3689   |-> cmpt 4170   -->wf 5347   ` cfv 5351  (class class class)co 6049   supcsup 7272  infcinf 7273   RRcr 8122   0cc0 8123   + caddc 8126   +oocpnf 8301   -oocmnf 8302   < clt 8304   - cmin 8440   (,]cioc 10218   [,)cico 10219

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-in1 619  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-10 1554  ax-11 1555  ax-i12 1556  ax-bndl 1558  ax-4 1559  ax-17 1575  ax-i9 1579  ax-ial 1583  ax-i5r 1584  ax-13 2205  ax-14 2206  ax-ext 2214  ax-coll 4224  ax-sep 4227  ax-nul 4235  ax-pow 4286  ax-pr 4321  ax-un 4553  ax-setind 4658  ax-iinf 4709  ax-cnex 8214  ax-resscn 8215  ax-1cn 8216  ax-1re 8217  ax-icn 8218  ax-addcl 8219  ax-addrcl 8220  ax-mulcl 8221  ax-mulrcl 8222  ax-addcom 8223  ax-mulcom 8224  ax-addass 8225  ax-mulass 8226  ax-distr 8227  ax-i2m1 8228  ax-0lt1 8229  ax-1rid 8230  ax-0id 8231  ax-rnegex 8232  ax-precex 8233  ax-cnre 8234  ax-pre-ltirr 8235  ax-pre-ltwlin 8236  ax-pre-lttrn 8237  ax-pre-apti 8238  ax-pre-ltadd 8239  ax-pre-mulgt0 8240  ax-pre-mulext 8241  ax-arch 8242  ax-caucvg 8243

This theorem depends on definitions:  df-bi 117  df-dc 843  df-3or 1006  df-3an 1007  df-tru 1401  df-fal 1404  df-nf 1510  df-sb 1812  df-eu 2083  df-mo 2084  df-clab 2219  df-cleq 2225  df-clel 2228  df-nfc 2373  df-ne 2413  df-nel 2508  df-ral 2525  df-rex 2526  df-reu 2527  df-rmo 2528  df-rab 2529  df-v 2814  df-sbc 3042  df-csb 3138  df-dif 3212  df-un 3214  df-in 3216  df-ss 3223  df-nul 3508  df-if 3620  df-pw 3670  df-sn 3694  df-pr 3695  df-op 3697  df-uni 3914  df-int 3949  df-iun 3992  df-br 4109  df-opab 4171  df-mpt 4172  df-tr 4208  df-id 4413  df-po 4416  df-iso 4417  df-iord 4486  df-on 4488  df-ilim 4489  df-suc 4491  df-iom 4712  df-xp 4754  df-rel 4755  df-cnv 4756  df-co 4757  df-dm 4758  df-rn 4759  df-res 4760  df-ima 4761  df-iota 5311  df-fun 5353  df-fn 5354  df-f 5355  df-f1 5356  df-fo 5357  df-f1o 5358  df-fv 5359  df-isom 5360  df-riota 6002  df-ov 6052  df-oprab 6053  df-mpo 6054  df-1st 6333  df-2nd 6334  df-recs 6535  df-frec 6621  df-sup 7274  df-inf 7275  df-pnf 8306  df-mnf 8307  df-xr 8308  df-ltxr 8309  df-le 8310  df-sub 8442  df-neg 8443  df-reap 8845  df-ap 8852  df-div 8943  df-inn 9234  df-2 9292  df-3 9293  df-4 9294  df-n0 9493  df-z 9574  df-uz 9850  df-rp 9983  df-ioc 10222  df-ico 10223  df-seqfrec 10806  df-exp 10897  df-cj 11520  df-re 11521  df-im 11522  df-rsqrt 11676  df-abs 11677

This theorem is referenced by: (None)