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Mirrors > Home > MPE Home > Th. List > sgnval | Structured version Visualization version GIF version |
Description: Value of Signum function. Pronounced "signum" . See df-sgn 13675. (Contributed by David A. Wheeler, 15-May-2015.) |
Ref | Expression |
---|---|
sgnval | ⊢ (𝐴 ∈ ℝ* → (sgn‘𝐴) = if(𝐴 = 0, 0, if(𝐴 < 0, -1, 1))) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | eqeq1 2614 | . . 3 ⊢ (𝑥 = 𝐴 → (𝑥 = 0 ↔ 𝐴 = 0)) | |
2 | breq1 4586 | . . . 4 ⊢ (𝑥 = 𝐴 → (𝑥 < 0 ↔ 𝐴 < 0)) | |
3 | 2 | ifbid 4058 | . . 3 ⊢ (𝑥 = 𝐴 → if(𝑥 < 0, -1, 1) = if(𝐴 < 0, -1, 1)) |
4 | 1, 3 | ifbieq2d 4061 | . 2 ⊢ (𝑥 = 𝐴 → if(𝑥 = 0, 0, if(𝑥 < 0, -1, 1)) = if(𝐴 = 0, 0, if(𝐴 < 0, -1, 1))) |
5 | df-sgn 13675 | . 2 ⊢ sgn = (𝑥 ∈ ℝ* ↦ if(𝑥 = 0, 0, if(𝑥 < 0, -1, 1))) | |
6 | c0ex 9913 | . . 3 ⊢ 0 ∈ V | |
7 | negex 10158 | . . . 4 ⊢ -1 ∈ V | |
8 | 1ex 9914 | . . . 4 ⊢ 1 ∈ V | |
9 | 7, 8 | ifex 4106 | . . 3 ⊢ if(𝐴 < 0, -1, 1) ∈ V |
10 | 6, 9 | ifex 4106 | . 2 ⊢ if(𝐴 = 0, 0, if(𝐴 < 0, -1, 1)) ∈ V |
11 | 4, 5, 10 | fvmpt 6191 | 1 ⊢ (𝐴 ∈ ℝ* → (sgn‘𝐴) = if(𝐴 = 0, 0, if(𝐴 < 0, -1, 1))) |
Colors of variables: wff setvar class |
Syntax hints: → wi 4 = wceq 1475 ∈ wcel 1977 ifcif 4036 class class class wbr 4583 ‘cfv 5804 0cc0 9815 1c1 9816 ℝ*cxr 9952 < clt 9953 -cneg 10146 sgncsgn 13674 |
This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-3 8 ax-gen 1713 ax-4 1728 ax-5 1827 ax-6 1875 ax-7 1922 ax-9 1986 ax-10 2006 ax-11 2021 ax-12 2034 ax-13 2234 ax-ext 2590 ax-sep 4709 ax-nul 4717 ax-pr 4833 ax-1cn 9873 ax-icn 9874 ax-addcl 9875 ax-mulcl 9877 ax-i2m1 9883 |
This theorem depends on definitions: df-bi 196 df-or 384 df-an 385 df-3an 1033 df-tru 1478 df-ex 1696 df-nf 1701 df-sb 1868 df-eu 2462 df-mo 2463 df-clab 2597 df-cleq 2603 df-clel 2606 df-nfc 2740 df-ral 2901 df-rex 2902 df-rab 2905 df-v 3175 df-sbc 3403 df-dif 3543 df-un 3545 df-in 3547 df-ss 3554 df-nul 3875 df-if 4037 df-sn 4126 df-pr 4128 df-op 4132 df-uni 4373 df-br 4584 df-opab 4644 df-mpt 4645 df-id 4953 df-xp 5044 df-rel 5045 df-cnv 5046 df-co 5047 df-dm 5048 df-iota 5768 df-fun 5806 df-fv 5812 df-ov 6552 df-neg 10148 df-sgn 13675 |
This theorem is referenced by: sgn0 13677 sgnp 13678 sgnn 13682 sgnneg 29929 sgn3da 29930 |
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