| Step | Hyp | Ref | Expression | 
|---|
| 1 |  | simpl2 1192 | . . 3
⊢ (((𝐾 ∈ 𝐷 ∧ 𝑄 ∈ 𝐴 ∧ 𝑅 ∈ 𝐴) ∧ (𝑄 ≠ 𝑅 ∧ 𝑋 = {𝑝 ∈ 𝐴 ∣ 𝑝 ≤ (𝑄 ∨ 𝑅)})) → 𝑄 ∈ 𝐴) | 
| 2 |  | simpl3 1193 | . . 3
⊢ (((𝐾 ∈ 𝐷 ∧ 𝑄 ∈ 𝐴 ∧ 𝑅 ∈ 𝐴) ∧ (𝑄 ≠ 𝑅 ∧ 𝑋 = {𝑝 ∈ 𝐴 ∣ 𝑝 ≤ (𝑄 ∨ 𝑅)})) → 𝑅 ∈ 𝐴) | 
| 3 |  | simpr 484 | . . 3
⊢ (((𝐾 ∈ 𝐷 ∧ 𝑄 ∈ 𝐴 ∧ 𝑅 ∈ 𝐴) ∧ (𝑄 ≠ 𝑅 ∧ 𝑋 = {𝑝 ∈ 𝐴 ∣ 𝑝 ≤ (𝑄 ∨ 𝑅)})) → (𝑄 ≠ 𝑅 ∧ 𝑋 = {𝑝 ∈ 𝐴 ∣ 𝑝 ≤ (𝑄 ∨ 𝑅)})) | 
| 4 |  | neeq1 3002 | . . . . 5
⊢ (𝑞 = 𝑄 → (𝑞 ≠ 𝑟 ↔ 𝑄 ≠ 𝑟)) | 
| 5 |  | oveq1 7439 | . . . . . . . 8
⊢ (𝑞 = 𝑄 → (𝑞 ∨ 𝑟) = (𝑄 ∨ 𝑟)) | 
| 6 | 5 | breq2d 5154 | . . . . . . 7
⊢ (𝑞 = 𝑄 → (𝑝 ≤ (𝑞 ∨ 𝑟) ↔ 𝑝 ≤ (𝑄 ∨ 𝑟))) | 
| 7 | 6 | rabbidv 3443 | . . . . . 6
⊢ (𝑞 = 𝑄 → {𝑝 ∈ 𝐴 ∣ 𝑝 ≤ (𝑞 ∨ 𝑟)} = {𝑝 ∈ 𝐴 ∣ 𝑝 ≤ (𝑄 ∨ 𝑟)}) | 
| 8 | 7 | eqeq2d 2747 | . . . . 5
⊢ (𝑞 = 𝑄 → (𝑋 = {𝑝 ∈ 𝐴 ∣ 𝑝 ≤ (𝑞 ∨ 𝑟)} ↔ 𝑋 = {𝑝 ∈ 𝐴 ∣ 𝑝 ≤ (𝑄 ∨ 𝑟)})) | 
| 9 | 4, 8 | anbi12d 632 | . . . 4
⊢ (𝑞 = 𝑄 → ((𝑞 ≠ 𝑟 ∧ 𝑋 = {𝑝 ∈ 𝐴 ∣ 𝑝 ≤ (𝑞 ∨ 𝑟)}) ↔ (𝑄 ≠ 𝑟 ∧ 𝑋 = {𝑝 ∈ 𝐴 ∣ 𝑝 ≤ (𝑄 ∨ 𝑟)}))) | 
| 10 |  | neeq2 3003 | . . . . 5
⊢ (𝑟 = 𝑅 → (𝑄 ≠ 𝑟 ↔ 𝑄 ≠ 𝑅)) | 
| 11 |  | oveq2 7440 | . . . . . . . 8
⊢ (𝑟 = 𝑅 → (𝑄 ∨ 𝑟) = (𝑄 ∨ 𝑅)) | 
| 12 | 11 | breq2d 5154 | . . . . . . 7
⊢ (𝑟 = 𝑅 → (𝑝 ≤ (𝑄 ∨ 𝑟) ↔ 𝑝 ≤ (𝑄 ∨ 𝑅))) | 
| 13 | 12 | rabbidv 3443 | . . . . . 6
⊢ (𝑟 = 𝑅 → {𝑝 ∈ 𝐴 ∣ 𝑝 ≤ (𝑄 ∨ 𝑟)} = {𝑝 ∈ 𝐴 ∣ 𝑝 ≤ (𝑄 ∨ 𝑅)}) | 
| 14 | 13 | eqeq2d 2747 | . . . . 5
⊢ (𝑟 = 𝑅 → (𝑋 = {𝑝 ∈ 𝐴 ∣ 𝑝 ≤ (𝑄 ∨ 𝑟)} ↔ 𝑋 = {𝑝 ∈ 𝐴 ∣ 𝑝 ≤ (𝑄 ∨ 𝑅)})) | 
| 15 | 10, 14 | anbi12d 632 | . . . 4
⊢ (𝑟 = 𝑅 → ((𝑄 ≠ 𝑟 ∧ 𝑋 = {𝑝 ∈ 𝐴 ∣ 𝑝 ≤ (𝑄 ∨ 𝑟)}) ↔ (𝑄 ≠ 𝑅 ∧ 𝑋 = {𝑝 ∈ 𝐴 ∣ 𝑝 ≤ (𝑄 ∨ 𝑅)}))) | 
| 16 | 9, 15 | rspc2ev 3634 | . . 3
⊢ ((𝑄 ∈ 𝐴 ∧ 𝑅 ∈ 𝐴 ∧ (𝑄 ≠ 𝑅 ∧ 𝑋 = {𝑝 ∈ 𝐴 ∣ 𝑝 ≤ (𝑄 ∨ 𝑅)})) → ∃𝑞 ∈ 𝐴 ∃𝑟 ∈ 𝐴 (𝑞 ≠ 𝑟 ∧ 𝑋 = {𝑝 ∈ 𝐴 ∣ 𝑝 ≤ (𝑞 ∨ 𝑟)})) | 
| 17 | 1, 2, 3, 16 | syl3anc 1372 | . 2
⊢ (((𝐾 ∈ 𝐷 ∧ 𝑄 ∈ 𝐴 ∧ 𝑅 ∈ 𝐴) ∧ (𝑄 ≠ 𝑅 ∧ 𝑋 = {𝑝 ∈ 𝐴 ∣ 𝑝 ≤ (𝑄 ∨ 𝑅)})) → ∃𝑞 ∈ 𝐴 ∃𝑟 ∈ 𝐴 (𝑞 ≠ 𝑟 ∧ 𝑋 = {𝑝 ∈ 𝐴 ∣ 𝑝 ≤ (𝑞 ∨ 𝑟)})) | 
| 18 |  | simpl1 1191 | . . 3
⊢ (((𝐾 ∈ 𝐷 ∧ 𝑄 ∈ 𝐴 ∧ 𝑅 ∈ 𝐴) ∧ (𝑄 ≠ 𝑅 ∧ 𝑋 = {𝑝 ∈ 𝐴 ∣ 𝑝 ≤ (𝑄 ∨ 𝑅)})) → 𝐾 ∈ 𝐷) | 
| 19 |  | isline.l | . . . 4
⊢  ≤ =
(le‘𝐾) | 
| 20 |  | isline.j | . . . 4
⊢  ∨ =
(join‘𝐾) | 
| 21 |  | isline.a | . . . 4
⊢ 𝐴 = (Atoms‘𝐾) | 
| 22 |  | isline.n | . . . 4
⊢ 𝑁 = (Lines‘𝐾) | 
| 23 | 19, 20, 21, 22 | isline 39742 | . . 3
⊢ (𝐾 ∈ 𝐷 → (𝑋 ∈ 𝑁 ↔ ∃𝑞 ∈ 𝐴 ∃𝑟 ∈ 𝐴 (𝑞 ≠ 𝑟 ∧ 𝑋 = {𝑝 ∈ 𝐴 ∣ 𝑝 ≤ (𝑞 ∨ 𝑟)}))) | 
| 24 | 18, 23 | syl 17 | . 2
⊢ (((𝐾 ∈ 𝐷 ∧ 𝑄 ∈ 𝐴 ∧ 𝑅 ∈ 𝐴) ∧ (𝑄 ≠ 𝑅 ∧ 𝑋 = {𝑝 ∈ 𝐴 ∣ 𝑝 ≤ (𝑄 ∨ 𝑅)})) → (𝑋 ∈ 𝑁 ↔ ∃𝑞 ∈ 𝐴 ∃𝑟 ∈ 𝐴 (𝑞 ≠ 𝑟 ∧ 𝑋 = {𝑝 ∈ 𝐴 ∣ 𝑝 ≤ (𝑞 ∨ 𝑟)}))) | 
| 25 | 17, 24 | mpbird 257 | 1
⊢ (((𝐾 ∈ 𝐷 ∧ 𝑄 ∈ 𝐴 ∧ 𝑅 ∈ 𝐴) ∧ (𝑄 ≠ 𝑅 ∧ 𝑋 = {𝑝 ∈ 𝐴 ∣ 𝑝 ≤ (𝑄 ∨ 𝑅)})) → 𝑋 ∈ 𝑁) |