Mathbox for Thierry Arnoux |
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Mirrors > Home > MPE Home > Th. List > Mathboxes > sgnsgn | Structured version Visualization version GIF version |
Description: Signum is idempotent. (Contributed by Thierry Arnoux, 2-Oct-2018.) |
Ref | Expression |
---|---|
sgnsgn | ⊢ (𝐴 ∈ ℝ* → (sgn‘(sgn‘𝐴)) = (sgn‘𝐴)) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | id 22 | . 2 ⊢ (𝐴 ∈ ℝ* → 𝐴 ∈ ℝ*) | |
2 | fveq2 6668 | . . 3 ⊢ ((sgn‘𝐴) = 0 → (sgn‘(sgn‘𝐴)) = (sgn‘0)) | |
3 | id 22 | . . 3 ⊢ ((sgn‘𝐴) = 0 → (sgn‘𝐴) = 0) | |
4 | 2, 3 | eqeq12d 2754 | . 2 ⊢ ((sgn‘𝐴) = 0 → ((sgn‘(sgn‘𝐴)) = (sgn‘𝐴) ↔ (sgn‘0) = 0)) |
5 | fveq2 6668 | . . 3 ⊢ ((sgn‘𝐴) = 1 → (sgn‘(sgn‘𝐴)) = (sgn‘1)) | |
6 | id 22 | . . 3 ⊢ ((sgn‘𝐴) = 1 → (sgn‘𝐴) = 1) | |
7 | 5, 6 | eqeq12d 2754 | . 2 ⊢ ((sgn‘𝐴) = 1 → ((sgn‘(sgn‘𝐴)) = (sgn‘𝐴) ↔ (sgn‘1) = 1)) |
8 | fveq2 6668 | . . 3 ⊢ ((sgn‘𝐴) = -1 → (sgn‘(sgn‘𝐴)) = (sgn‘-1)) | |
9 | id 22 | . . 3 ⊢ ((sgn‘𝐴) = -1 → (sgn‘𝐴) = -1) | |
10 | 8, 9 | eqeq12d 2754 | . 2 ⊢ ((sgn‘𝐴) = -1 → ((sgn‘(sgn‘𝐴)) = (sgn‘𝐴) ↔ (sgn‘-1) = -1)) |
11 | sgn0 14531 | . . 3 ⊢ (sgn‘0) = 0 | |
12 | 11 | a1i 11 | . 2 ⊢ ((𝐴 ∈ ℝ* ∧ 𝐴 = 0) → (sgn‘0) = 0) |
13 | sgn1 14534 | . . 3 ⊢ (sgn‘1) = 1 | |
14 | 13 | a1i 11 | . 2 ⊢ ((𝐴 ∈ ℝ* ∧ 0 < 𝐴) → (sgn‘1) = 1) |
15 | neg1rr 11824 | . . . . 5 ⊢ -1 ∈ ℝ | |
16 | 15 | rexri 10770 | . . . 4 ⊢ -1 ∈ ℝ* |
17 | neg1lt0 11826 | . . . 4 ⊢ -1 < 0 | |
18 | sgnn 14536 | . . . 4 ⊢ ((-1 ∈ ℝ* ∧ -1 < 0) → (sgn‘-1) = -1) | |
19 | 16, 17, 18 | mp2an 692 | . . 3 ⊢ (sgn‘-1) = -1 |
20 | 19 | a1i 11 | . 2 ⊢ ((𝐴 ∈ ℝ* ∧ 𝐴 < 0) → (sgn‘-1) = -1) |
21 | 1, 4, 7, 10, 12, 14, 20 | sgn3da 32070 | 1 ⊢ (𝐴 ∈ ℝ* → (sgn‘(sgn‘𝐴)) = (sgn‘𝐴)) |
Colors of variables: wff setvar class |
Syntax hints: → wi 4 ∧ wa 399 = wceq 1542 ∈ wcel 2113 class class class wbr 5027 ‘cfv 6333 0cc0 10608 1c1 10609 ℝ*cxr 10745 < clt 10746 -cneg 10942 sgncsgn 14528 |
This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-3 8 ax-gen 1802 ax-4 1816 ax-5 1916 ax-6 1974 ax-7 2019 ax-8 2115 ax-9 2123 ax-10 2144 ax-11 2161 ax-12 2178 ax-ext 2710 ax-sep 5164 ax-nul 5171 ax-pow 5229 ax-pr 5293 ax-un 7473 ax-cnex 10664 ax-resscn 10665 ax-1cn 10666 ax-icn 10667 ax-addcl 10668 ax-addrcl 10669 ax-mulcl 10670 ax-mulrcl 10671 ax-mulcom 10672 ax-addass 10673 ax-mulass 10674 ax-distr 10675 ax-i2m1 10676 ax-1ne0 10677 ax-1rid 10678 ax-rnegex 10679 ax-rrecex 10680 ax-cnre 10681 ax-pre-lttri 10682 ax-pre-lttrn 10683 ax-pre-ltadd 10684 ax-pre-mulgt0 10685 |
This theorem depends on definitions: df-bi 210 df-an 400 df-or 847 df-3or 1089 df-3an 1090 df-tru 1545 df-fal 1555 df-ex 1787 df-nf 1791 df-sb 2074 df-mo 2540 df-eu 2570 df-clab 2717 df-cleq 2730 df-clel 2811 df-nfc 2881 df-ne 2935 df-nel 3039 df-ral 3058 df-rex 3059 df-reu 3060 df-rab 3062 df-v 3399 df-sbc 3680 df-csb 3789 df-dif 3844 df-un 3846 df-in 3848 df-ss 3858 df-nul 4210 df-if 4412 df-pw 4487 df-sn 4514 df-pr 4516 df-op 4520 df-uni 4794 df-br 5028 df-opab 5090 df-mpt 5108 df-id 5425 df-po 5438 df-so 5439 df-xp 5525 df-rel 5526 df-cnv 5527 df-co 5528 df-dm 5529 df-rn 5530 df-res 5531 df-ima 5532 df-iota 6291 df-fun 6335 df-fn 6336 df-f 6337 df-f1 6338 df-fo 6339 df-f1o 6340 df-fv 6341 df-riota 7121 df-ov 7167 df-oprab 7168 df-mpo 7169 df-er 8313 df-en 8549 df-dom 8550 df-sdom 8551 df-pnf 10748 df-mnf 10749 df-xr 10750 df-ltxr 10751 df-le 10752 df-sub 10943 df-neg 10944 df-sgn 14529 |
This theorem is referenced by: signsvfn 32123 signsvfpn 32126 signsvfnn 32127 |
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