| Step | Hyp | Ref
 | Expression | 
| 1 |   | ltrelpr 7572 | 
. . . 4
⊢
<P ⊆ (P ×
P) | 
| 2 | 1 | brel 4715 | 
. . 3
⊢ (𝐴<P
𝐵 → (𝐴 ∈ P ∧ 𝐵 ∈
P)) | 
| 3 |   | ltdfpr 7573 | 
. . . 4
⊢ ((𝐴 ∈ P ∧
𝐵 ∈ P)
→ (𝐴<P 𝐵 ↔ ∃𝑥 ∈ Q (𝑥 ∈ (2nd
‘𝐴) ∧ 𝑥 ∈ (1st
‘𝐵)))) | 
| 4 | 3 | biimpd 144 | 
. . 3
⊢ ((𝐴 ∈ P ∧
𝐵 ∈ P)
→ (𝐴<P 𝐵 → ∃𝑥 ∈ Q (𝑥 ∈ (2nd
‘𝐴) ∧ 𝑥 ∈ (1st
‘𝐵)))) | 
| 5 | 2, 4 | mpcom 36 | 
. 2
⊢ (𝐴<P
𝐵 → ∃𝑥 ∈ Q (𝑥 ∈ (2nd
‘𝐴) ∧ 𝑥 ∈ (1st
‘𝐵))) | 
| 6 |   | simpll 527 | 
. . . . . 6
⊢ (((𝐴<P
𝐵 ∧ (𝑥 ∈ Q ∧ (𝑥 ∈ (2nd
‘𝐴) ∧ 𝑥 ∈ (1st
‘𝐵)))) ∧ 𝑦 ∈ (1st
‘𝐴)) → 𝐴<P
𝐵) | 
| 7 |   | simpr 110 | 
. . . . . 6
⊢ (((𝐴<P
𝐵 ∧ (𝑥 ∈ Q ∧ (𝑥 ∈ (2nd
‘𝐴) ∧ 𝑥 ∈ (1st
‘𝐵)))) ∧ 𝑦 ∈ (1st
‘𝐴)) → 𝑦 ∈ (1st
‘𝐴)) | 
| 8 |   | simprrl 539 | 
. . . . . . 7
⊢ ((𝐴<P
𝐵 ∧ (𝑥 ∈ Q ∧ (𝑥 ∈ (2nd
‘𝐴) ∧ 𝑥 ∈ (1st
‘𝐵)))) → 𝑥 ∈ (2nd
‘𝐴)) | 
| 9 | 8 | adantr 276 | 
. . . . . 6
⊢ (((𝐴<P
𝐵 ∧ (𝑥 ∈ Q ∧ (𝑥 ∈ (2nd
‘𝐴) ∧ 𝑥 ∈ (1st
‘𝐵)))) ∧ 𝑦 ∈ (1st
‘𝐴)) → 𝑥 ∈ (2nd
‘𝐴)) | 
| 10 | 2 | simpld 112 | 
. . . . . . . 8
⊢ (𝐴<P
𝐵 → 𝐴 ∈ P) | 
| 11 |   | prop 7542 | 
. . . . . . . 8
⊢ (𝐴 ∈ P →
〈(1st ‘𝐴), (2nd ‘𝐴)〉 ∈
P) | 
| 12 | 10, 11 | syl 14 | 
. . . . . . 7
⊢ (𝐴<P
𝐵 →
〈(1st ‘𝐴), (2nd ‘𝐴)〉 ∈
P) | 
| 13 |   | prltlu 7554 | 
. . . . . . 7
⊢
((〈(1st ‘𝐴), (2nd ‘𝐴)〉 ∈ P ∧ 𝑦 ∈ (1st
‘𝐴) ∧ 𝑥 ∈ (2nd
‘𝐴)) → 𝑦 <Q
𝑥) | 
| 14 | 12, 13 | syl3an1 1282 | 
. . . . . 6
⊢ ((𝐴<P
𝐵 ∧ 𝑦 ∈ (1st ‘𝐴) ∧ 𝑥 ∈ (2nd ‘𝐴)) → 𝑦 <Q 𝑥) | 
| 15 | 6, 7, 9, 14 | syl3anc 1249 | 
. . . . 5
⊢ (((𝐴<P
𝐵 ∧ (𝑥 ∈ Q ∧ (𝑥 ∈ (2nd
‘𝐴) ∧ 𝑥 ∈ (1st
‘𝐵)))) ∧ 𝑦 ∈ (1st
‘𝐴)) → 𝑦 <Q
𝑥) | 
| 16 |   | simprrr 540 | 
. . . . . . 7
⊢ ((𝐴<P
𝐵 ∧ (𝑥 ∈ Q ∧ (𝑥 ∈ (2nd
‘𝐴) ∧ 𝑥 ∈ (1st
‘𝐵)))) → 𝑥 ∈ (1st
‘𝐵)) | 
| 17 | 16 | adantr 276 | 
. . . . . 6
⊢ (((𝐴<P
𝐵 ∧ (𝑥 ∈ Q ∧ (𝑥 ∈ (2nd
‘𝐴) ∧ 𝑥 ∈ (1st
‘𝐵)))) ∧ 𝑦 ∈ (1st
‘𝐴)) → 𝑥 ∈ (1st
‘𝐵)) | 
| 18 | 2 | simprd 114 | 
. . . . . . . 8
⊢ (𝐴<P
𝐵 → 𝐵 ∈ P) | 
| 19 |   | prop 7542 | 
. . . . . . . 8
⊢ (𝐵 ∈ P →
〈(1st ‘𝐵), (2nd ‘𝐵)〉 ∈
P) | 
| 20 | 18, 19 | syl 14 | 
. . . . . . 7
⊢ (𝐴<P
𝐵 →
〈(1st ‘𝐵), (2nd ‘𝐵)〉 ∈
P) | 
| 21 |   | prcdnql 7551 | 
. . . . . . 7
⊢
((〈(1st ‘𝐵), (2nd ‘𝐵)〉 ∈ P ∧ 𝑥 ∈ (1st
‘𝐵)) → (𝑦 <Q
𝑥 → 𝑦 ∈ (1st ‘𝐵))) | 
| 22 | 20, 21 | sylan 283 | 
. . . . . 6
⊢ ((𝐴<P
𝐵 ∧ 𝑥 ∈ (1st ‘𝐵)) → (𝑦 <Q 𝑥 → 𝑦 ∈ (1st ‘𝐵))) | 
| 23 | 6, 17, 22 | syl2anc 411 | 
. . . . 5
⊢ (((𝐴<P
𝐵 ∧ (𝑥 ∈ Q ∧ (𝑥 ∈ (2nd
‘𝐴) ∧ 𝑥 ∈ (1st
‘𝐵)))) ∧ 𝑦 ∈ (1st
‘𝐴)) → (𝑦 <Q
𝑥 → 𝑦 ∈ (1st ‘𝐵))) | 
| 24 | 15, 23 | mpd 13 | 
. . . 4
⊢ (((𝐴<P
𝐵 ∧ (𝑥 ∈ Q ∧ (𝑥 ∈ (2nd
‘𝐴) ∧ 𝑥 ∈ (1st
‘𝐵)))) ∧ 𝑦 ∈ (1st
‘𝐴)) → 𝑦 ∈ (1st
‘𝐵)) | 
| 25 | 24 | ex 115 | 
. . 3
⊢ ((𝐴<P
𝐵 ∧ (𝑥 ∈ Q ∧ (𝑥 ∈ (2nd
‘𝐴) ∧ 𝑥 ∈ (1st
‘𝐵)))) → (𝑦 ∈ (1st
‘𝐴) → 𝑦 ∈ (1st
‘𝐵))) | 
| 26 | 25 | ssrdv 3189 | 
. 2
⊢ ((𝐴<P
𝐵 ∧ (𝑥 ∈ Q ∧ (𝑥 ∈ (2nd
‘𝐴) ∧ 𝑥 ∈ (1st
‘𝐵)))) →
(1st ‘𝐴)
⊆ (1st ‘𝐵)) | 
| 27 | 5, 26 | rexlimddv 2619 | 
1
⊢ (𝐴<P
𝐵 → (1st
‘𝐴) ⊆
(1st ‘𝐵)) |