Theorem dceqnconst 14847

Description: Decidability of real number equality implies the existence of a certain non-constant function from real numbers to integers. Variation of Exercise 11.6(i) of [HoTT], p. (varies). See redcwlpo 14842 for more discussion of decidability of real number equality. (Contributed by BJ and Jim Kingdon, 24-Jun-2024.) (Revised by Jim Kingdon, 23-Jul-2024.)

Assertion

Ref	Expression
dceqnconst	|- ( A. x e. RR DECID x = 0 -> E. f ( f : RR --> ZZ /\ ( f ` 0 ) = 0 /\ A. x e. RR+ ( f ` x ) =/= 0 ) )

Distinct variable group:   x, f

Proof of Theorem dceqnconst

Dummy variables y z are mutually distinct and distinct from all other variables.

Step	Hyp	Ref	Expression
1		reex 7947	. . . 4 |- RR e. _V
2	1	mptex 5744	. . 3 |- ( y e. RR |-> if ( y = 0 , 0 , 1 ) ) e. _V
3	2	a1i 9	. 2 |- ( A. x e. RR DECID x = 0 -> ( y e. RR |-> if ( y = 0 , 0 , 1 ) ) e. _V )
4		0zd 9267	. . . . 5 |- ( ( A. x e. RR DECID x = 0 /\ y e. RR ) -> 0 e. ZZ )
5		1zzd 9282	. . . . 5 |- ( ( A. x e. RR DECID x = 0 /\ y e. RR ) -> 1 e. ZZ )
6		eqeq1 2184	. . . . . . 7 |- ( x = y -> ( x = 0 <-> y = 0 ) )
7	6	dcbid 838	. . . . . 6 |- ( x = y -> (DECID x = 0 <-> DECID y = 0 ) )
8	7	rspccva 2842	. . . . 5 |- ( ( A. x e. RR DECID x = 0 /\ y e. RR ) -> DECID y = 0 )
9	4, 5, 8	ifcldcd 3572	. . . 4 |- ( ( A. x e. RR DECID x = 0 /\ y e. RR ) -> if ( y = 0 , 0 , 1 ) e. ZZ )
10	9	fmpttd 5673	. . 3 |- ( A. x e. RR DECID x = 0 -> ( y e. RR |-> if ( y = 0 , 0 , 1 ) ) : RR --> ZZ )
11		0re 7959	. . . . . 6 |- 0 e. RR
12		0zd 9267	. . . . . . . 8 |- ( T. -> 0 e. ZZ )
13		1zzd 9282	. . . . . . . 8 |- ( T. -> 1 e. ZZ )
14		eqid 2177	. . . . . . . . . . 11 |- 0 = 0
15	14	orci 731	. . . . . . . . . 10 |- ( 0 = 0 \/ -. 0 = 0 )
16		df-dc 835	. . . . . . . . . 10 |- (DECID 0 = 0 <-> ( 0 = 0 \/ -. 0 = 0 ) )
17	15, 16	mpbir 146	. . . . . . . . 9 |- DECID 0 = 0
18	17	a1i 9	. . . . . . . 8 |- ( T. -> DECID 0 = 0 )
19	12, 13, 18	ifcldcd 3572	. . . . . . 7 |- ( T. -> if ( 0 = 0 , 0 , 1 ) e. ZZ )
20	19	mptru 1362	. . . . . 6 |- if ( 0 = 0 , 0 , 1 ) e. ZZ
21		eqeq1 2184	. . . . . . . 8 |- ( y = 0 -> ( y = 0 <-> 0 = 0 ) )
22	21	ifbid 3557	. . . . . . 7 |- ( y = 0 -> if ( y = 0 , 0 , 1 ) = if ( 0 = 0 , 0 , 1 ) )
23		eqid 2177	. . . . . . 7 |- ( y e. RR |-> if ( y = 0 , 0 , 1 ) ) = ( y e. RR |-> if ( y = 0 , 0 , 1 ) )
24	22, 23	fvmptg 5594	. . . . . 6 |- ( ( 0 e. RR /\ if ( 0 = 0 , 0 , 1 ) e. ZZ ) -> ( ( y e. RR |-> if ( y = 0 , 0 , 1 ) ) ` 0 ) = if ( 0 = 0 , 0 , 1 ) )
25	11, 20, 24	mp2an 426	. . . . 5 |- ( ( y e. RR |-> if ( y = 0 , 0 , 1 ) ) ` 0 ) = if ( 0 = 0 , 0 , 1 )
26	14	iftruei 3542	. . . . 5 |- if ( 0 = 0 , 0 , 1 ) = 0
27	25, 26	eqtri 2198	. . . 4 |- ( ( y e. RR |-> if ( y = 0 , 0 , 1 ) ) ` 0 ) = 0
28	27	a1i 9	. . 3 |- ( A. x e. RR DECID x = 0 -> ( ( y e. RR |-> if ( y = 0 , 0 , 1 ) ) ` 0 ) = 0 )
29		1ne0 8989	. . . . . 6 |- 1 =/= 0
30		eqeq1 2184	. . . . . . . . . 10 |- ( y = z -> ( y = 0 <-> z = 0 ) )
31	30	ifbid 3557	. . . . . . . . 9 |- ( y = z -> if ( y = 0 , 0 , 1 ) = if ( z = 0 , 0 , 1 ) )
32		rpre 9662	. . . . . . . . . 10 |- ( z e. RR+ -> z e. RR )
33	32	adantl 277	. . . . . . . . 9 |- ( ( A. x e. RR DECID x = 0 /\ z e. RR+ ) -> z e. RR )
34		0zd 9267	. . . . . . . . . 10 |- ( ( A. x e. RR DECID x = 0 /\ z e. RR+ ) -> 0 e. ZZ )
35		1zzd 9282	. . . . . . . . . 10 |- ( ( A. x e. RR DECID x = 0 /\ z e. RR+ ) -> 1 e. ZZ )
36		eqeq1 2184	. . . . . . . . . . . 12 |- ( x = z -> ( x = 0 <-> z = 0 ) )
37	36	dcbid 838	. . . . . . . . . . 11 |- ( x = z -> (DECID x = 0 <-> DECID z = 0 ) )
38		simpl 109	. . . . . . . . . . 11 |- ( ( A. x e. RR DECID x = 0 /\ z e. RR+ ) -> A. x e. RR DECID x = 0 )
39	37, 38, 33	rspcdva 2848	. . . . . . . . . 10 |- ( ( A. x e. RR DECID x = 0 /\ z e. RR+ ) -> DECID z = 0 )
40	34, 35, 39	ifcldcd 3572	. . . . . . . . 9 |- ( ( A. x e. RR DECID x = 0 /\ z e. RR+ ) -> if ( z = 0 , 0 , 1 ) e. ZZ )
41	23, 31, 33, 40	fvmptd3 5611	. . . . . . . 8 |- ( ( A. x e. RR DECID x = 0 /\ z e. RR+ ) -> ( ( y e. RR |-> if ( y = 0 , 0 , 1 ) ) ` z ) = if ( z = 0 , 0 , 1 ) )
42		rpne0 9671	. . . . . . . . . . 11 |- ( z e. RR+ -> z =/= 0 )
43	42	neneqd 2368	. . . . . . . . . 10 |- ( z e. RR+ -> -. z = 0 )
44	43	iffalsed 3546	. . . . . . . . 9 |- ( z e. RR+ -> if ( z = 0 , 0 , 1 ) = 1 )
45	44	adantl 277	. . . . . . . 8 |- ( ( A. x e. RR DECID x = 0 /\ z e. RR+ ) -> if ( z = 0 , 0 , 1 ) = 1 )
46	41, 45	eqtrd 2210	. . . . . . 7 |- ( ( A. x e. RR DECID x = 0 /\ z e. RR+ ) -> ( ( y e. RR |-> if ( y = 0 , 0 , 1 ) ) ` z ) = 1 )
47	46	neeq1d 2365	. . . . . 6 |- ( ( A. x e. RR DECID x = 0 /\ z e. RR+ ) -> ( ( ( y e. RR |-> if ( y = 0 , 0 , 1 ) ) ` z ) =/= 0 <-> 1 =/= 0 ) )
48	29, 47	mpbiri 168	. . . . 5 |- ( ( A. x e. RR DECID x = 0 /\ z e. RR+ ) -> ( ( y e. RR |-> if ( y = 0 , 0 , 1 ) ) ` z ) =/= 0 )
49	48	ralrimiva 2550	. . . 4 |- ( A. x e. RR DECID x = 0 -> A. z e. RR+ ( ( y e. RR |-> if ( y = 0 , 0 , 1 ) ) ` z ) =/= 0 )
50		fveq2 5517	. . . . . 6 |- ( z = x -> ( ( y e. RR |-> if ( y = 0 , 0 , 1 ) ) ` z ) = ( ( y e. RR |-> if ( y = 0 , 0 , 1 ) ) ` x ) )
51	50	neeq1d 2365	. . . . 5 |- ( z = x -> ( ( ( y e. RR |-> if ( y = 0 , 0 , 1 ) ) ` z ) =/= 0 <-> ( ( y e. RR |-> if ( y = 0 , 0 , 1 ) ) ` x ) =/= 0 ) )
52	51	cbvralv 2705	. . . 4 |- ( A. z e. RR+ ( ( y e. RR |-> if ( y = 0 , 0 , 1 ) ) ` z ) =/= 0 <-> A. x e. RR+ ( ( y e. RR |-> if ( y = 0 , 0 , 1 ) ) ` x ) =/= 0 )
53	49, 52	sylib 122	. . 3 |- ( A. x e. RR DECID x = 0 -> A. x e. RR+ ( ( y e. RR |-> if ( y = 0 , 0 , 1 ) ) ` x ) =/= 0 )
54	10, 28, 53	3jca 1177	. 2 |- ( A. x e. RR DECID x = 0 -> ( ( y e. RR |-> if ( y = 0 , 0 , 1 ) ) : RR --> ZZ /\ ( ( y e. RR |-> if ( y = 0 , 0 , 1 ) ) ` 0 ) = 0 /\ A. x e. RR+ ( ( y e. RR |-> if ( y = 0 , 0 , 1 ) ) ` x ) =/= 0 ) )
55		feq1 5350	. . 3 |- ( f = ( y e. RR |-> if ( y = 0 , 0 , 1 ) ) -> ( f : RR --> ZZ <-> ( y e. RR |-> if ( y = 0 , 0 , 1 ) ) : RR --> ZZ ) )
56		fveq1 5516	. . . 4 |- ( f = ( y e. RR |-> if ( y = 0 , 0 , 1 ) ) -> ( f ` 0 ) = ( ( y e. RR |-> if ( y = 0 , 0 , 1 ) ) ` 0 ) )
57	56	eqeq1d 2186	. . 3 |- ( f = ( y e. RR |-> if ( y = 0 , 0 , 1 ) ) -> ( ( f ` 0 ) = 0 <-> ( ( y e. RR |-> if ( y = 0 , 0 , 1 ) ) ` 0 ) = 0 ) )
58		fveq1 5516	. . . . 5 |- ( f = ( y e. RR |-> if ( y = 0 , 0 , 1 ) ) -> ( f ` x ) = ( ( y e. RR |-> if ( y = 0 , 0 , 1 ) ) ` x ) )
59	58	neeq1d 2365	. . . 4 |- ( f = ( y e. RR |-> if ( y = 0 , 0 , 1 ) ) -> ( ( f ` x ) =/= 0 <-> ( ( y e. RR |-> if ( y = 0 , 0 , 1 ) ) ` x ) =/= 0 ) )
60	59	ralbidv 2477	. . 3 |- ( f = ( y e. RR |-> if ( y = 0 , 0 , 1 ) ) -> ( A. x e. RR+ ( f ` x ) =/= 0 <-> A. x e. RR+ ( ( y e. RR |-> if ( y = 0 , 0 , 1 ) ) ` x ) =/= 0 ) )
61	55, 57, 60	3anbi123d 1312	. 2 |- ( f = ( y e. RR |-> if ( y = 0 , 0 , 1 ) ) -> ( ( f : RR --> ZZ /\ ( f ` 0 ) = 0 /\ A. x e. RR+ ( f ` x ) =/= 0 ) <-> ( ( y e. RR |-> if ( y = 0 , 0 , 1 ) ) : RR --> ZZ /\ ( ( y e. RR |-> if ( y = 0 , 0 , 1 ) ) ` 0 ) = 0 /\ A. x e. RR+ ( ( y e. RR |-> if ( y = 0 , 0 , 1 ) ) ` x ) =/= 0 ) ) )
62	3, 54, 61	elabd 2884	1 |- ( A. x e. RR DECID x = 0 -> E. f ( f : RR --> ZZ /\ ( f ` 0 ) = 0 /\ A. x e. RR+ ( f ` x ) =/= 0 ) )

Syntax hints:   -. wn 3   -> wi 4   /\ wa 104   \/ wo 708  DECID wdc 834   /\ w3a 978   = wceq 1353   T. wtru 1354   E.wex 1492   e. wcel 2148   =/= wne 2347   A.wral 2455   _Vcvv 2739   ifcif 3536   |-> cmpt 4066   -->wf 5214   ` cfv 5218   RRcr 7812   0cc0 7813   1c1 7814   ZZcz 9255   RR+crp 9655

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 614  ax-in2 615  ax-io 709  ax-5 1447  ax-7 1448  ax-gen 1449  ax-ie1 1493  ax-ie2 1494  ax-8 1504  ax-10 1505  ax-11 1506  ax-i12 1507  ax-bndl 1509  ax-4 1510  ax-17 1526  ax-i9 1530  ax-ial 1534  ax-i5r 1535  ax-13 2150  ax-14 2151  ax-ext 2159  ax-coll 4120  ax-sep 4123  ax-pow 4176  ax-pr 4211  ax-un 4435  ax-setind 4538  ax-cnex 7904  ax-resscn 7905  ax-1cn 7906  ax-1re 7907  ax-icn 7908  ax-addcl 7909  ax-addrcl 7910  ax-mulcl 7911  ax-addcom 7913  ax-addass 7915  ax-distr 7917  ax-i2m1 7918  ax-0lt1 7919  ax-0id 7921  ax-rnegex 7922  ax-cnre 7924  ax-pre-ltirr 7925  ax-pre-ltwlin 7926  ax-pre-lttrn 7927  ax-pre-ltadd 7929

This theorem depends on definitions:  df-bi 117  df-dc 835  df-3or 979  df-3an 980  df-tru 1356  df-fal 1359  df-nf 1461  df-sb 1763  df-eu 2029  df-mo 2030  df-clab 2164  df-cleq 2170  df-clel 2173  df-nfc 2308  df-ne 2348  df-nel 2443  df-ral 2460  df-rex 2461  df-reu 2462  df-rab 2464  df-v 2741  df-sbc 2965  df-csb 3060  df-dif 3133  df-un 3135  df-in 3137  df-ss 3144  df-if 3537  df-pw 3579  df-sn 3600  df-pr 3601  df-op 3603  df-uni 3812  df-int 3847  df-iun 3890  df-br 4006  df-opab 4067  df-mpt 4068  df-id 4295  df-xp 4634  df-rel 4635  df-cnv 4636  df-co 4637  df-dm 4638  df-rn 4639  df-res 4640  df-ima 4641  df-iota 5180  df-fun 5220  df-fn 5221  df-f 5222  df-f1 5223  df-fo 5224  df-f1o 5225  df-fv 5226  df-riota 5833  df-ov 5880  df-oprab 5881  df-mpo 5882  df-pnf 7996  df-mnf 7997  df-xr 7998  df-ltxr 7999  df-le 8000  df-sub 8132  df-neg 8133  df-inn 8922  df-z 9256  df-rp 9656

This theorem is referenced by:  dcapnconstALT  14849