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Description: Lemma for 3at . (Contributed by NM, 23-Jun-2012)
| Ref | Expression | ||
|---|---|---|---|
| Hypotheses | 3at.l | |- .<_ = ( le ` K ) |
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| 3at.j | |- .\/ = ( join ` K ) |
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| 3at.a | |- A = ( Atoms ` K ) |
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| Assertion | 3atlem5 | |- ( ( ( K e. HL /\ ( P e. A /\ Q e. A /\ R e. A ) /\ ( S e. A /\ T e. A /\ U e. A ) ) /\ ( -. R .<_ ( P .\/ Q ) /\ P =/= Q /\ -. Q .<_ ( P .\/ U ) ) /\ ( ( P .\/ Q ) .\/ R ) .<_ ( ( S .\/ T ) .\/ U ) ) -> ( ( P .\/ Q ) .\/ R ) = ( ( S .\/ T ) .\/ U ) ) |
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 1 | 3at.l | |- .<_ = ( le ` K ) |
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| 2 | 3at.j | |- .\/ = ( join ` K ) |
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| 3 | 3at.a | |- A = ( Atoms ` K ) |
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| 4 | oveq2 | |- ( U = P -> ( ( S .\/ T ) .\/ U ) = ( ( S .\/ T ) .\/ P ) ) |
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| 5 | 4 | eqcoms | |- ( P = U -> ( ( S .\/ T ) .\/ U ) = ( ( S .\/ T ) .\/ P ) ) |
| 6 | 5 | breq2d | |- ( P = U -> ( ( ( P .\/ Q ) .\/ R ) .<_ ( ( S .\/ T ) .\/ U ) <-> ( ( P .\/ Q ) .\/ R ) .<_ ( ( S .\/ T ) .\/ P ) ) ) |
| 7 | 5 | eqeq2d | |- ( P = U -> ( ( ( P .\/ Q ) .\/ R ) = ( ( S .\/ T ) .\/ U ) <-> ( ( P .\/ Q ) .\/ R ) = ( ( S .\/ T ) .\/ P ) ) ) |
| 8 | 6 7 | imbi12d | |- ( P = U -> ( ( ( ( P .\/ Q ) .\/ R ) .<_ ( ( S .\/ T ) .\/ U ) -> ( ( P .\/ Q ) .\/ R ) = ( ( S .\/ T ) .\/ U ) ) <-> ( ( ( P .\/ Q ) .\/ R ) .<_ ( ( S .\/ T ) .\/ P ) -> ( ( P .\/ Q ) .\/ R ) = ( ( S .\/ T ) .\/ P ) ) ) ) |
| 9 | simp1l | |- ( ( ( ( K e. HL /\ ( P e. A /\ Q e. A /\ R e. A ) /\ ( S e. A /\ T e. A /\ U e. A ) ) /\ ( -. R .<_ ( P .\/ Q ) /\ P =/= Q /\ -. Q .<_ ( P .\/ U ) ) ) /\ P =/= U /\ ( ( P .\/ Q ) .\/ R ) .<_ ( ( S .\/ T ) .\/ U ) ) -> ( K e. HL /\ ( P e. A /\ Q e. A /\ R e. A ) /\ ( S e. A /\ T e. A /\ U e. A ) ) ) |
|
| 10 | simp1r1 | |- ( ( ( ( K e. HL /\ ( P e. A /\ Q e. A /\ R e. A ) /\ ( S e. A /\ T e. A /\ U e. A ) ) /\ ( -. R .<_ ( P .\/ Q ) /\ P =/= Q /\ -. Q .<_ ( P .\/ U ) ) ) /\ P =/= U /\ ( ( P .\/ Q ) .\/ R ) .<_ ( ( S .\/ T ) .\/ U ) ) -> -. R .<_ ( P .\/ Q ) ) |
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| 11 | simp2 | |- ( ( ( ( K e. HL /\ ( P e. A /\ Q e. A /\ R e. A ) /\ ( S e. A /\ T e. A /\ U e. A ) ) /\ ( -. R .<_ ( P .\/ Q ) /\ P =/= Q /\ -. Q .<_ ( P .\/ U ) ) ) /\ P =/= U /\ ( ( P .\/ Q ) .\/ R ) .<_ ( ( S .\/ T ) .\/ U ) ) -> P =/= U ) |
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| 12 | simp1r3 | |- ( ( ( ( K e. HL /\ ( P e. A /\ Q e. A /\ R e. A ) /\ ( S e. A /\ T e. A /\ U e. A ) ) /\ ( -. R .<_ ( P .\/ Q ) /\ P =/= Q /\ -. Q .<_ ( P .\/ U ) ) ) /\ P =/= U /\ ( ( P .\/ Q ) .\/ R ) .<_ ( ( S .\/ T ) .\/ U ) ) -> -. Q .<_ ( P .\/ U ) ) |
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| 13 | simp3 | |- ( ( ( ( K e. HL /\ ( P e. A /\ Q e. A /\ R e. A ) /\ ( S e. A /\ T e. A /\ U e. A ) ) /\ ( -. R .<_ ( P .\/ Q ) /\ P =/= Q /\ -. Q .<_ ( P .\/ U ) ) ) /\ P =/= U /\ ( ( P .\/ Q ) .\/ R ) .<_ ( ( S .\/ T ) .\/ U ) ) -> ( ( P .\/ Q ) .\/ R ) .<_ ( ( S .\/ T ) .\/ U ) ) |
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| 14 | 1 2 3 | 3atlem3 | |- ( ( ( K e. HL /\ ( P e. A /\ Q e. A /\ R e. A ) /\ ( S e. A /\ T e. A /\ U e. A ) ) /\ ( -. R .<_ ( P .\/ Q ) /\ P =/= U /\ -. Q .<_ ( P .\/ U ) ) /\ ( ( P .\/ Q ) .\/ R ) .<_ ( ( S .\/ T ) .\/ U ) ) -> ( ( P .\/ Q ) .\/ R ) = ( ( S .\/ T ) .\/ U ) ) |
| 15 | 9 10 11 12 13 14 | syl131anc | |- ( ( ( ( K e. HL /\ ( P e. A /\ Q e. A /\ R e. A ) /\ ( S e. A /\ T e. A /\ U e. A ) ) /\ ( -. R .<_ ( P .\/ Q ) /\ P =/= Q /\ -. Q .<_ ( P .\/ U ) ) ) /\ P =/= U /\ ( ( P .\/ Q ) .\/ R ) .<_ ( ( S .\/ T ) .\/ U ) ) -> ( ( P .\/ Q ) .\/ R ) = ( ( S .\/ T ) .\/ U ) ) |
| 16 | 15 | 3expia | |- ( ( ( ( K e. HL /\ ( P e. A /\ Q e. A /\ R e. A ) /\ ( S e. A /\ T e. A /\ U e. A ) ) /\ ( -. R .<_ ( P .\/ Q ) /\ P =/= Q /\ -. Q .<_ ( P .\/ U ) ) ) /\ P =/= U ) -> ( ( ( P .\/ Q ) .\/ R ) .<_ ( ( S .\/ T ) .\/ U ) -> ( ( P .\/ Q ) .\/ R ) = ( ( S .\/ T ) .\/ U ) ) ) |
| 17 | simp11 | |- ( ( ( K e. HL /\ ( P e. A /\ Q e. A /\ R e. A ) /\ ( S e. A /\ T e. A /\ U e. A ) ) /\ ( -. R .<_ ( P .\/ Q ) /\ P =/= Q /\ -. Q .<_ ( P .\/ U ) ) /\ ( ( R .\/ Q ) .\/ P ) .<_ ( ( S .\/ T ) .\/ P ) ) -> K e. HL ) |
|
| 18 | simp123 | |- ( ( ( K e. HL /\ ( P e. A /\ Q e. A /\ R e. A ) /\ ( S e. A /\ T e. A /\ U e. A ) ) /\ ( -. R .<_ ( P .\/ Q ) /\ P =/= Q /\ -. Q .<_ ( P .\/ U ) ) /\ ( ( R .\/ Q ) .\/ P ) .<_ ( ( S .\/ T ) .\/ P ) ) -> R e. A ) |
|
| 19 | simp122 | |- ( ( ( K e. HL /\ ( P e. A /\ Q e. A /\ R e. A ) /\ ( S e. A /\ T e. A /\ U e. A ) ) /\ ( -. R .<_ ( P .\/ Q ) /\ P =/= Q /\ -. Q .<_ ( P .\/ U ) ) /\ ( ( R .\/ Q ) .\/ P ) .<_ ( ( S .\/ T ) .\/ P ) ) -> Q e. A ) |
|
| 20 | simp121 | |- ( ( ( K e. HL /\ ( P e. A /\ Q e. A /\ R e. A ) /\ ( S e. A /\ T e. A /\ U e. A ) ) /\ ( -. R .<_ ( P .\/ Q ) /\ P =/= Q /\ -. Q .<_ ( P .\/ U ) ) /\ ( ( R .\/ Q ) .\/ P ) .<_ ( ( S .\/ T ) .\/ P ) ) -> P e. A ) |
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| 21 | 18 19 20 | 3jca | |- ( ( ( K e. HL /\ ( P e. A /\ Q e. A /\ R e. A ) /\ ( S e. A /\ T e. A /\ U e. A ) ) /\ ( -. R .<_ ( P .\/ Q ) /\ P =/= Q /\ -. Q .<_ ( P .\/ U ) ) /\ ( ( R .\/ Q ) .\/ P ) .<_ ( ( S .\/ T ) .\/ P ) ) -> ( R e. A /\ Q e. A /\ P e. A ) ) |
| 22 | simp131 | |- ( ( ( K e. HL /\ ( P e. A /\ Q e. A /\ R e. A ) /\ ( S e. A /\ T e. A /\ U e. A ) ) /\ ( -. R .<_ ( P .\/ Q ) /\ P =/= Q /\ -. Q .<_ ( P .\/ U ) ) /\ ( ( R .\/ Q ) .\/ P ) .<_ ( ( S .\/ T ) .\/ P ) ) -> S e. A ) |
|
| 23 | simp132 | |- ( ( ( K e. HL /\ ( P e. A /\ Q e. A /\ R e. A ) /\ ( S e. A /\ T e. A /\ U e. A ) ) /\ ( -. R .<_ ( P .\/ Q ) /\ P =/= Q /\ -. Q .<_ ( P .\/ U ) ) /\ ( ( R .\/ Q ) .\/ P ) .<_ ( ( S .\/ T ) .\/ P ) ) -> T e. A ) |
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| 24 | 22 23 | jca | |- ( ( ( K e. HL /\ ( P e. A /\ Q e. A /\ R e. A ) /\ ( S e. A /\ T e. A /\ U e. A ) ) /\ ( -. R .<_ ( P .\/ Q ) /\ P =/= Q /\ -. Q .<_ ( P .\/ U ) ) /\ ( ( R .\/ Q ) .\/ P ) .<_ ( ( S .\/ T ) .\/ P ) ) -> ( S e. A /\ T e. A ) ) |
| 25 | simp21 | |- ( ( ( K e. HL /\ ( P e. A /\ Q e. A /\ R e. A ) /\ ( S e. A /\ T e. A /\ U e. A ) ) /\ ( -. R .<_ ( P .\/ Q ) /\ P =/= Q /\ -. Q .<_ ( P .\/ U ) ) /\ ( ( R .\/ Q ) .\/ P ) .<_ ( ( S .\/ T ) .\/ P ) ) -> -. R .<_ ( P .\/ Q ) ) |
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| 26 | simp22 | |- ( ( ( K e. HL /\ ( P e. A /\ Q e. A /\ R e. A ) /\ ( S e. A /\ T e. A /\ U e. A ) ) /\ ( -. R .<_ ( P .\/ Q ) /\ P =/= Q /\ -. Q .<_ ( P .\/ U ) ) /\ ( ( R .\/ Q ) .\/ P ) .<_ ( ( S .\/ T ) .\/ P ) ) -> P =/= Q ) |
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| 27 | 1 2 3 | hlatexch2 | |- ( ( K e. HL /\ ( P e. A /\ R e. A /\ Q e. A ) /\ P =/= Q ) -> ( P .<_ ( R .\/ Q ) -> R .<_ ( P .\/ Q ) ) ) |
| 28 | 17 20 18 19 26 27 | syl131anc | |- ( ( ( K e. HL /\ ( P e. A /\ Q e. A /\ R e. A ) /\ ( S e. A /\ T e. A /\ U e. A ) ) /\ ( -. R .<_ ( P .\/ Q ) /\ P =/= Q /\ -. Q .<_ ( P .\/ U ) ) /\ ( ( R .\/ Q ) .\/ P ) .<_ ( ( S .\/ T ) .\/ P ) ) -> ( P .<_ ( R .\/ Q ) -> R .<_ ( P .\/ Q ) ) ) |
| 29 | 25 28 | mtod | |- ( ( ( K e. HL /\ ( P e. A /\ Q e. A /\ R e. A ) /\ ( S e. A /\ T e. A /\ U e. A ) ) /\ ( -. R .<_ ( P .\/ Q ) /\ P =/= Q /\ -. Q .<_ ( P .\/ U ) ) /\ ( ( R .\/ Q ) .\/ P ) .<_ ( ( S .\/ T ) .\/ P ) ) -> -. P .<_ ( R .\/ Q ) ) |
| 30 | 17 | hllatd | |- ( ( ( K e. HL /\ ( P e. A /\ Q e. A /\ R e. A ) /\ ( S e. A /\ T e. A /\ U e. A ) ) /\ ( -. R .<_ ( P .\/ Q ) /\ P =/= Q /\ -. Q .<_ ( P .\/ U ) ) /\ ( ( R .\/ Q ) .\/ P ) .<_ ( ( S .\/ T ) .\/ P ) ) -> K e. Lat ) |
| 31 | eqid | |- ( Base ` K ) = ( Base ` K ) |
|
| 32 | 31 3 | atbase | |- ( R e. A -> R e. ( Base ` K ) ) |
| 33 | 18 32 | syl | |- ( ( ( K e. HL /\ ( P e. A /\ Q e. A /\ R e. A ) /\ ( S e. A /\ T e. A /\ U e. A ) ) /\ ( -. R .<_ ( P .\/ Q ) /\ P =/= Q /\ -. Q .<_ ( P .\/ U ) ) /\ ( ( R .\/ Q ) .\/ P ) .<_ ( ( S .\/ T ) .\/ P ) ) -> R e. ( Base ` K ) ) |
| 34 | 31 3 | atbase | |- ( P e. A -> P e. ( Base ` K ) ) |
| 35 | 20 34 | syl | |- ( ( ( K e. HL /\ ( P e. A /\ Q e. A /\ R e. A ) /\ ( S e. A /\ T e. A /\ U e. A ) ) /\ ( -. R .<_ ( P .\/ Q ) /\ P =/= Q /\ -. Q .<_ ( P .\/ U ) ) /\ ( ( R .\/ Q ) .\/ P ) .<_ ( ( S .\/ T ) .\/ P ) ) -> P e. ( Base ` K ) ) |
| 36 | 31 3 | atbase | |- ( Q e. A -> Q e. ( Base ` K ) ) |
| 37 | 19 36 | syl | |- ( ( ( K e. HL /\ ( P e. A /\ Q e. A /\ R e. A ) /\ ( S e. A /\ T e. A /\ U e. A ) ) /\ ( -. R .<_ ( P .\/ Q ) /\ P =/= Q /\ -. Q .<_ ( P .\/ U ) ) /\ ( ( R .\/ Q ) .\/ P ) .<_ ( ( S .\/ T ) .\/ P ) ) -> Q e. ( Base ` K ) ) |
| 38 | 31 1 2 | latnlej1r | |- ( ( K e. Lat /\ ( R e. ( Base ` K ) /\ P e. ( Base ` K ) /\ Q e. ( Base ` K ) ) /\ -. R .<_ ( P .\/ Q ) ) -> R =/= Q ) |
| 39 | 30 33 35 37 25 38 | syl131anc | |- ( ( ( K e. HL /\ ( P e. A /\ Q e. A /\ R e. A ) /\ ( S e. A /\ T e. A /\ U e. A ) ) /\ ( -. R .<_ ( P .\/ Q ) /\ P =/= Q /\ -. Q .<_ ( P .\/ U ) ) /\ ( ( R .\/ Q ) .\/ P ) .<_ ( ( S .\/ T ) .\/ P ) ) -> R =/= Q ) |
| 40 | simp3 | |- ( ( ( K e. HL /\ ( P e. A /\ Q e. A /\ R e. A ) /\ ( S e. A /\ T e. A /\ U e. A ) ) /\ ( -. R .<_ ( P .\/ Q ) /\ P =/= Q /\ -. Q .<_ ( P .\/ U ) ) /\ ( ( R .\/ Q ) .\/ P ) .<_ ( ( S .\/ T ) .\/ P ) ) -> ( ( R .\/ Q ) .\/ P ) .<_ ( ( S .\/ T ) .\/ P ) ) |
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| 41 | 1 2 3 | 3atlem4 | |- ( ( ( K e. HL /\ ( R e. A /\ Q e. A /\ P e. A ) /\ ( S e. A /\ T e. A ) ) /\ ( -. P .<_ ( R .\/ Q ) /\ R =/= Q ) /\ ( ( R .\/ Q ) .\/ P ) .<_ ( ( S .\/ T ) .\/ P ) ) -> ( ( R .\/ Q ) .\/ P ) = ( ( S .\/ T ) .\/ P ) ) |
| 42 | 17 21 24 29 39 40 41 | syl321anc | |- ( ( ( K e. HL /\ ( P e. A /\ Q e. A /\ R e. A ) /\ ( S e. A /\ T e. A /\ U e. A ) ) /\ ( -. R .<_ ( P .\/ Q ) /\ P =/= Q /\ -. Q .<_ ( P .\/ U ) ) /\ ( ( R .\/ Q ) .\/ P ) .<_ ( ( S .\/ T ) .\/ P ) ) -> ( ( R .\/ Q ) .\/ P ) = ( ( S .\/ T ) .\/ P ) ) |
| 43 | 42 | 3expia | |- ( ( ( K e. HL /\ ( P e. A /\ Q e. A /\ R e. A ) /\ ( S e. A /\ T e. A /\ U e. A ) ) /\ ( -. R .<_ ( P .\/ Q ) /\ P =/= Q /\ -. Q .<_ ( P .\/ U ) ) ) -> ( ( ( R .\/ Q ) .\/ P ) .<_ ( ( S .\/ T ) .\/ P ) -> ( ( R .\/ Q ) .\/ P ) = ( ( S .\/ T ) .\/ P ) ) ) |
| 44 | simpl1 | |- ( ( ( K e. HL /\ ( P e. A /\ Q e. A /\ R e. A ) /\ ( S e. A /\ T e. A /\ U e. A ) ) /\ ( -. R .<_ ( P .\/ Q ) /\ P =/= Q /\ -. Q .<_ ( P .\/ U ) ) ) -> K e. HL ) |
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| 45 | 44 | hllatd | |- ( ( ( K e. HL /\ ( P e. A /\ Q e. A /\ R e. A ) /\ ( S e. A /\ T e. A /\ U e. A ) ) /\ ( -. R .<_ ( P .\/ Q ) /\ P =/= Q /\ -. Q .<_ ( P .\/ U ) ) ) -> K e. Lat ) |
| 46 | simpl21 | |- ( ( ( K e. HL /\ ( P e. A /\ Q e. A /\ R e. A ) /\ ( S e. A /\ T e. A /\ U e. A ) ) /\ ( -. R .<_ ( P .\/ Q ) /\ P =/= Q /\ -. Q .<_ ( P .\/ U ) ) ) -> P e. A ) |
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| 47 | 46 34 | syl | |- ( ( ( K e. HL /\ ( P e. A /\ Q e. A /\ R e. A ) /\ ( S e. A /\ T e. A /\ U e. A ) ) /\ ( -. R .<_ ( P .\/ Q ) /\ P =/= Q /\ -. Q .<_ ( P .\/ U ) ) ) -> P e. ( Base ` K ) ) |
| 48 | simpl22 | |- ( ( ( K e. HL /\ ( P e. A /\ Q e. A /\ R e. A ) /\ ( S e. A /\ T e. A /\ U e. A ) ) /\ ( -. R .<_ ( P .\/ Q ) /\ P =/= Q /\ -. Q .<_ ( P .\/ U ) ) ) -> Q e. A ) |
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| 49 | 48 36 | syl | |- ( ( ( K e. HL /\ ( P e. A /\ Q e. A /\ R e. A ) /\ ( S e. A /\ T e. A /\ U e. A ) ) /\ ( -. R .<_ ( P .\/ Q ) /\ P =/= Q /\ -. Q .<_ ( P .\/ U ) ) ) -> Q e. ( Base ` K ) ) |
| 50 | simpl23 | |- ( ( ( K e. HL /\ ( P e. A /\ Q e. A /\ R e. A ) /\ ( S e. A /\ T e. A /\ U e. A ) ) /\ ( -. R .<_ ( P .\/ Q ) /\ P =/= Q /\ -. Q .<_ ( P .\/ U ) ) ) -> R e. A ) |
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| 51 | 50 32 | syl | |- ( ( ( K e. HL /\ ( P e. A /\ Q e. A /\ R e. A ) /\ ( S e. A /\ T e. A /\ U e. A ) ) /\ ( -. R .<_ ( P .\/ Q ) /\ P =/= Q /\ -. Q .<_ ( P .\/ U ) ) ) -> R e. ( Base ` K ) ) |
| 52 | 31 2 | latj31 | |- ( ( K e. Lat /\ ( P e. ( Base ` K ) /\ Q e. ( Base ` K ) /\ R e. ( Base ` K ) ) ) -> ( ( P .\/ Q ) .\/ R ) = ( ( R .\/ Q ) .\/ P ) ) |
| 53 | 45 47 49 51 52 | syl13anc | |- ( ( ( K e. HL /\ ( P e. A /\ Q e. A /\ R e. A ) /\ ( S e. A /\ T e. A /\ U e. A ) ) /\ ( -. R .<_ ( P .\/ Q ) /\ P =/= Q /\ -. Q .<_ ( P .\/ U ) ) ) -> ( ( P .\/ Q ) .\/ R ) = ( ( R .\/ Q ) .\/ P ) ) |
| 54 | 53 | breq1d | |- ( ( ( K e. HL /\ ( P e. A /\ Q e. A /\ R e. A ) /\ ( S e. A /\ T e. A /\ U e. A ) ) /\ ( -. R .<_ ( P .\/ Q ) /\ P =/= Q /\ -. Q .<_ ( P .\/ U ) ) ) -> ( ( ( P .\/ Q ) .\/ R ) .<_ ( ( S .\/ T ) .\/ P ) <-> ( ( R .\/ Q ) .\/ P ) .<_ ( ( S .\/ T ) .\/ P ) ) ) |
| 55 | 53 | eqeq1d | |- ( ( ( K e. HL /\ ( P e. A /\ Q e. A /\ R e. A ) /\ ( S e. A /\ T e. A /\ U e. A ) ) /\ ( -. R .<_ ( P .\/ Q ) /\ P =/= Q /\ -. Q .<_ ( P .\/ U ) ) ) -> ( ( ( P .\/ Q ) .\/ R ) = ( ( S .\/ T ) .\/ P ) <-> ( ( R .\/ Q ) .\/ P ) = ( ( S .\/ T ) .\/ P ) ) ) |
| 56 | 43 54 55 | 3imtr4d | |- ( ( ( K e. HL /\ ( P e. A /\ Q e. A /\ R e. A ) /\ ( S e. A /\ T e. A /\ U e. A ) ) /\ ( -. R .<_ ( P .\/ Q ) /\ P =/= Q /\ -. Q .<_ ( P .\/ U ) ) ) -> ( ( ( P .\/ Q ) .\/ R ) .<_ ( ( S .\/ T ) .\/ P ) -> ( ( P .\/ Q ) .\/ R ) = ( ( S .\/ T ) .\/ P ) ) ) |
| 57 | 8 16 56 | pm2.61ne | |- ( ( ( K e. HL /\ ( P e. A /\ Q e. A /\ R e. A ) /\ ( S e. A /\ T e. A /\ U e. A ) ) /\ ( -. R .<_ ( P .\/ Q ) /\ P =/= Q /\ -. Q .<_ ( P .\/ U ) ) ) -> ( ( ( P .\/ Q ) .\/ R ) .<_ ( ( S .\/ T ) .\/ U ) -> ( ( P .\/ Q ) .\/ R ) = ( ( S .\/ T ) .\/ U ) ) ) |
| 58 | 57 | 3impia | |- ( ( ( K e. HL /\ ( P e. A /\ Q e. A /\ R e. A ) /\ ( S e. A /\ T e. A /\ U e. A ) ) /\ ( -. R .<_ ( P .\/ Q ) /\ P =/= Q /\ -. Q .<_ ( P .\/ U ) ) /\ ( ( P .\/ Q ) .\/ R ) .<_ ( ( S .\/ T ) .\/ U ) ) -> ( ( P .\/ Q ) .\/ R ) = ( ( S .\/ T ) .\/ U ) ) |