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Theorem sscon 3077
 Description: Contraposition law for subsets. Exercise 15 of [TakeutiZaring] p. 22. (Contributed by NM, 22-Mar-1998.)
Assertion
Ref Expression
sscon

Proof of Theorem sscon
Dummy variable is distinct from all other variables.
StepHypRef Expression
1 ssel 2939 . . . . 5
21con3d 561 . . . 4
32anim2d 320 . . 3
4 eldif 2927 . . 3
5 eldif 2927 . . 3
63, 4, 53imtr4g 194 . 2
76ssrdv 2951 1
 Colors of variables: wff set class Syntax hints:   wn 3   wi 4   wa 97   wcel 1393   cdif 2914   wss 2917 This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 99  ax-ia2 100  ax-ia3 101  ax-in1 544  ax-in2 545  ax-io 630  ax-5 1336  ax-7 1337  ax-gen 1338  ax-ie1 1382  ax-ie2 1383  ax-8 1395  ax-10 1396  ax-11 1397  ax-i12 1398  ax-bndl 1399  ax-4 1400  ax-17 1419  ax-i9 1423  ax-ial 1427  ax-i5r 1428  ax-ext 2022 This theorem depends on definitions:  df-bi 110  df-tru 1246  df-nf 1350  df-sb 1646  df-clab 2027  df-cleq 2033  df-clel 2036  df-nfc 2167  df-v 2559  df-dif 2920  df-in 2924  df-ss 2931 This theorem is referenced by:  sscond  3080
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