Theorem repiecef 17089

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 17087 and repiecege0 17088. 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. 17088 (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 17086	. . . 4 |- ( ( ph /\ y e. RR ) -> ( ( ( F ` inf ( { y , 0 } , RR , < ) ) + ( G ` sup ( { y , 0 } , RR , < ) ) ) - ( F ` 0 ) ) e. RR )
6	5	ralrimiva 2623	. . 3 |- ( ph -> A. y e. RR ( ( ( F ` inf ( { y , 0 } , RR , < ) ) + ( G ` sup ( { y , 0 } , RR , < ) ) ) - ( F ` 0 ) ) e. RR )
7		preq1 3788	. . . . . . . . 9 |- ( y = x -> { y , 0 } = { x , 0 } )
8	7	infeq1d 7352	. . . . . . . 8 |- ( y = x -> inf ( { y , 0 } , RR , < ) = inf ( { x , 0 } , RR , < ) )
9	8	fveq2d 5699	. . . . . . 7 |- ( y = x -> ( F ` inf ( { y , 0 } , RR , < ) ) = ( F ` inf ( { x , 0 } , RR , < ) ) )
10	7	supeq1d 7327	. . . . . . . 8 |- ( y = x -> sup ( { y , 0 } , RR , < ) = sup ( { x , 0 } , RR , < ) )
11	10	fveq2d 5699	. . . . . . 7 |- ( y = x -> ( G ` sup ( { y , 0 } , RR , < ) ) = ( G ` sup ( { x , 0 } , RR , < ) ) )
12	9, 11	oveq12d 6103	. . . . . 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 6100	. . . . 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 2307	. . . 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 2786	. . 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 5858	. 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 )

This proof depends on syntax axioms:   -> wi 4   = wceq 1402   e. wcel 2209   A.wral 2528   {cpr 3710   |-> cmpt 4192   -->wf 5373   ` cfv 5377  (class class class)co 6085   supcsup 7322  infcinf 7323   RRcr 8178   0cc0 8179   + caddc 8182   +oocpnf 8357   -oocmnf 8358   < clt 8360   - cmin 8497   (,]cioc 10293   [,)cico 10294

This proof depends on axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 106  ax-ia2 107  ax-ia3 108  ax-in1 623  ax-in2 624  ax-io 721  ax-5 1500  ax-7 1501  ax-gen 1502  ax-ie1 1546  ax-ie2 1547  ax-8 1557  ax-10 1558  ax-11 1559  ax-i12 1560  ax-bndl 1562  ax-4 1563  ax-17 1579  ax-i9 1583  ax-ial 1587  ax-i5r 1588  ax-14 2212  ax-ext 2220  ax-coll 4246  ax-sep 4249  ax-nul 4259  ax-pow 4311  ax-pr 4346  ax-un 4578  ax-setind 4684  ax-iinf 4735  ax-cnex 8270  ax-resscn 8271  ax-1cn 8272  ax-1re 8273  ax-icn 8274  ax-addcl 8275  ax-addrcl 8276  ax-mulcl 8277  ax-mulrcl 8278  ax-addcom 8279  ax-mulcom 8280  ax-addass 8281  ax-mulass 8282  ax-distr 8283  ax-i2m1 8284  ax-0lt1 8285  ax-1rid 8286  ax-0id 8287  ax-rnegex 8288  ax-precex 8289  ax-cnre 8290  ax-pre-ltirr 8291  ax-pre-ltwlin 8292  ax-pre-lttrn 8293  ax-pre-apti 8294  ax-pre-ltadd 8295  ax-pre-mulgt0 8296  ax-pre-mulext 8297  ax-arch 8298  ax-caucvg 8299

This proof depends on definitions:  df-bi 117  df-dc 847  df-3or 1010  df-3an 1011  df-tru 1405  df-fal 1408  df-nf 1514  df-sb 1816  df-eu 2089  df-mo 2090  df-clab 2225  df-cleq 2231  df-clel 2234  df-nfc 2381  df-ne 2421  df-nel 2516  df-ral 2533  df-rex 2534  df-reu 2535  df-rmo 2536  df-rab 2537  df-v 2823  df-sbc 3052  df-csb 3148  df-dif 3222  df-un 3224  df-in 3226  df-ss 3233  df-nul 3521  df-if 3639  df-pw 3690  df-sn 3715  df-pr 3716  df-op 3718  df-uni 3936  df-int 3971  df-iun 4014  df-br 4131  df-opab 4193  df-mpt 4194  df-tr 4230  df-id 4438  df-po 4441  df-iso 4442  df-iord 4511  df-on 4513  df-ilim 4514  df-suc 4516  df-iom 4738  df-xp 4780  df-rel 4781  df-cnv 4782  df-co 4783  df-dm 4784  df-rn 4785  df-res 4786  df-ima 4787  df-iota 5337  df-fun 5379  df-fn 5380  df-f 5381  df-f1 5382  df-fo 5383  df-f1o 5384  df-fv 5385  df-isom 5386  df-riota 6038  df-ov 6088  df-oprab 6089  df-mpo 6090  df-1st 6374  df-2nd 6375  df-recs 6576  df-frec 6662  df-sup 7324  df-inf 7325  df-pnf 8362  df-mnf 8363  df-xr 8364  df-ltxr 8365  df-le 8366  df-sub 8499  df-neg 8500  df-reap 8904  df-ap 8911  df-div 9004  df-inn 9306  df-2 9364  df-3 9365  df-4 9366  df-n0 9566  df-z 9647  df-uz 9924  df-rp 10057  df-ioc 10297  df-ico 10298  df-seqfrec 10887  df-exp 10978  df-cj 11609  df-re 11610  df-im 11611  df-rsqrt 11766  df-abs 11767

This theorem is used by: (None)