| Step | Hyp | Ref
 | Expression | 
| 1 |   | exfzdc.1 | 
. . . . 5
⊢ (𝜑 → 𝑀 ∈ ℤ) | 
| 2 |   | exfzdc.2 | 
. . . . 5
⊢ (𝜑 → 𝑁 ∈ ℤ) | 
| 3 |   | eluz 9614 | 
. . . . 5
⊢ ((𝑀 ∈ ℤ ∧ 𝑁 ∈ ℤ) → (𝑁 ∈
(ℤ≥‘𝑀) ↔ 𝑀 ≤ 𝑁)) | 
| 4 | 1, 2, 3 | syl2anc 411 | 
. . . 4
⊢ (𝜑 → (𝑁 ∈ (ℤ≥‘𝑀) ↔ 𝑀 ≤ 𝑁)) | 
| 5 | 4 | biimpar 297 | 
. . 3
⊢ ((𝜑 ∧ 𝑀 ≤ 𝑁) → 𝑁 ∈ (ℤ≥‘𝑀)) | 
| 6 |   | simpl 109 | 
. . 3
⊢ ((𝜑 ∧ 𝑀 ≤ 𝑁) → 𝜑) | 
| 7 |   | eluzfz2 10107 | 
. . . 4
⊢ (𝑁 ∈
(ℤ≥‘𝑀) → 𝑁 ∈ (𝑀...𝑁)) | 
| 8 |   | oveq2 5930 | 
. . . . . . . 8
⊢ (𝑤 = 𝑀 → (𝑀...𝑤) = (𝑀...𝑀)) | 
| 9 | 8 | rexeqdv 2700 | 
. . . . . . 7
⊢ (𝑤 = 𝑀 → (∃𝑛 ∈ (𝑀...𝑤)𝜓 ↔ ∃𝑛 ∈ (𝑀...𝑀)𝜓)) | 
| 10 | 9 | dcbid 839 | 
. . . . . 6
⊢ (𝑤 = 𝑀 → (DECID ∃𝑛 ∈ (𝑀...𝑤)𝜓 ↔ DECID ∃𝑛 ∈ (𝑀...𝑀)𝜓)) | 
| 11 | 10 | imbi2d 230 | 
. . . . 5
⊢ (𝑤 = 𝑀 → ((𝜑 → DECID ∃𝑛 ∈ (𝑀...𝑤)𝜓) ↔ (𝜑 → DECID ∃𝑛 ∈ (𝑀...𝑀)𝜓))) | 
| 12 |   | oveq2 5930 | 
. . . . . . . 8
⊢ (𝑤 = 𝑦 → (𝑀...𝑤) = (𝑀...𝑦)) | 
| 13 | 12 | rexeqdv 2700 | 
. . . . . . 7
⊢ (𝑤 = 𝑦 → (∃𝑛 ∈ (𝑀...𝑤)𝜓 ↔ ∃𝑛 ∈ (𝑀...𝑦)𝜓)) | 
| 14 | 13 | dcbid 839 | 
. . . . . 6
⊢ (𝑤 = 𝑦 → (DECID ∃𝑛 ∈ (𝑀...𝑤)𝜓 ↔ DECID ∃𝑛 ∈ (𝑀...𝑦)𝜓)) | 
| 15 | 14 | imbi2d 230 | 
. . . . 5
⊢ (𝑤 = 𝑦 → ((𝜑 → DECID ∃𝑛 ∈ (𝑀...𝑤)𝜓) ↔ (𝜑 → DECID ∃𝑛 ∈ (𝑀...𝑦)𝜓))) | 
| 16 |   | oveq2 5930 | 
. . . . . . . 8
⊢ (𝑤 = (𝑦 + 1) → (𝑀...𝑤) = (𝑀...(𝑦 + 1))) | 
| 17 | 16 | rexeqdv 2700 | 
. . . . . . 7
⊢ (𝑤 = (𝑦 + 1) → (∃𝑛 ∈ (𝑀...𝑤)𝜓 ↔ ∃𝑛 ∈ (𝑀...(𝑦 + 1))𝜓)) | 
| 18 | 17 | dcbid 839 | 
. . . . . 6
⊢ (𝑤 = (𝑦 + 1) → (DECID
∃𝑛 ∈ (𝑀...𝑤)𝜓 ↔ DECID ∃𝑛 ∈ (𝑀...(𝑦 + 1))𝜓)) | 
| 19 | 18 | imbi2d 230 | 
. . . . 5
⊢ (𝑤 = (𝑦 + 1) → ((𝜑 → DECID ∃𝑛 ∈ (𝑀...𝑤)𝜓) ↔ (𝜑 → DECID ∃𝑛 ∈ (𝑀...(𝑦 + 1))𝜓))) | 
| 20 |   | oveq2 5930 | 
. . . . . . . 8
⊢ (𝑤 = 𝑁 → (𝑀...𝑤) = (𝑀...𝑁)) | 
| 21 | 20 | rexeqdv 2700 | 
. . . . . . 7
⊢ (𝑤 = 𝑁 → (∃𝑛 ∈ (𝑀...𝑤)𝜓 ↔ ∃𝑛 ∈ (𝑀...𝑁)𝜓)) | 
| 22 | 21 | dcbid 839 | 
. . . . . 6
⊢ (𝑤 = 𝑁 → (DECID ∃𝑛 ∈ (𝑀...𝑤)𝜓 ↔ DECID ∃𝑛 ∈ (𝑀...𝑁)𝜓)) | 
| 23 | 22 | imbi2d 230 | 
. . . . 5
⊢ (𝑤 = 𝑁 → ((𝜑 → DECID ∃𝑛 ∈ (𝑀...𝑤)𝜓) ↔ (𝜑 → DECID ∃𝑛 ∈ (𝑀...𝑁)𝜓))) | 
| 24 |   | eluzfz1 10106 | 
. . . . . . . . 9
⊢ (𝑁 ∈
(ℤ≥‘𝑀) → 𝑀 ∈ (𝑀...𝑁)) | 
| 25 | 24 | adantl 277 | 
. . . . . . . 8
⊢ ((𝜑 ∧ 𝑁 ∈ (ℤ≥‘𝑀)) → 𝑀 ∈ (𝑀...𝑁)) | 
| 26 |   | exfzdc.3 | 
. . . . . . . . . 10
⊢ ((𝜑 ∧ 𝑛 ∈ (𝑀...𝑁)) → DECID 𝜓) | 
| 27 | 26 | ralrimiva 2570 | 
. . . . . . . . 9
⊢ (𝜑 → ∀𝑛 ∈ (𝑀...𝑁)DECID 𝜓) | 
| 28 | 27 | adantr 276 | 
. . . . . . . 8
⊢ ((𝜑 ∧ 𝑁 ∈ (ℤ≥‘𝑀)) → ∀𝑛 ∈ (𝑀...𝑁)DECID 𝜓) | 
| 29 |   | nfsbc1v 3008 | 
. . . . . . . . . 10
⊢
Ⅎ𝑛[𝑀 / 𝑛]𝜓 | 
| 30 | 29 | nfdc 1673 | 
. . . . . . . . 9
⊢
Ⅎ𝑛DECID [𝑀 / 𝑛]𝜓 | 
| 31 |   | sbceq1a 2999 | 
. . . . . . . . . 10
⊢ (𝑛 = 𝑀 → (𝜓 ↔ [𝑀 / 𝑛]𝜓)) | 
| 32 | 31 | dcbid 839 | 
. . . . . . . . 9
⊢ (𝑛 = 𝑀 → (DECID 𝜓 ↔ DECID
[𝑀 / 𝑛]𝜓)) | 
| 33 | 30, 32 | rspc 2862 | 
. . . . . . . 8
⊢ (𝑀 ∈ (𝑀...𝑁) → (∀𝑛 ∈ (𝑀...𝑁)DECID 𝜓 → DECID [𝑀 / 𝑛]𝜓)) | 
| 34 | 25, 28, 33 | sylc 62 | 
. . . . . . 7
⊢ ((𝜑 ∧ 𝑁 ∈ (ℤ≥‘𝑀)) → DECID
[𝑀 / 𝑛]𝜓) | 
| 35 | 1 | adantr 276 | 
. . . . . . . . . . 11
⊢ ((𝜑 ∧ 𝑁 ∈ (ℤ≥‘𝑀)) → 𝑀 ∈ ℤ) | 
| 36 |   | fzsn 10141 | 
. . . . . . . . . . 11
⊢ (𝑀 ∈ ℤ → (𝑀...𝑀) = {𝑀}) | 
| 37 | 35, 36 | syl 14 | 
. . . . . . . . . 10
⊢ ((𝜑 ∧ 𝑁 ∈ (ℤ≥‘𝑀)) → (𝑀...𝑀) = {𝑀}) | 
| 38 | 37 | rexeqdv 2700 | 
. . . . . . . . 9
⊢ ((𝜑 ∧ 𝑁 ∈ (ℤ≥‘𝑀)) → (∃𝑛 ∈ (𝑀...𝑀)𝜓 ↔ ∃𝑛 ∈ {𝑀}𝜓)) | 
| 39 |   | rexsns 3661 | 
. . . . . . . . 9
⊢
(∃𝑛 ∈
{𝑀}𝜓 ↔ [𝑀 / 𝑛]𝜓) | 
| 40 | 38, 39 | bitrdi 196 | 
. . . . . . . 8
⊢ ((𝜑 ∧ 𝑁 ∈ (ℤ≥‘𝑀)) → (∃𝑛 ∈ (𝑀...𝑀)𝜓 ↔ [𝑀 / 𝑛]𝜓)) | 
| 41 | 40 | dcbid 839 | 
. . . . . . 7
⊢ ((𝜑 ∧ 𝑁 ∈ (ℤ≥‘𝑀)) → (DECID
∃𝑛 ∈ (𝑀...𝑀)𝜓 ↔ DECID [𝑀 / 𝑛]𝜓)) | 
| 42 | 34, 41 | mpbird 167 | 
. . . . . 6
⊢ ((𝜑 ∧ 𝑁 ∈ (ℤ≥‘𝑀)) → DECID
∃𝑛 ∈ (𝑀...𝑀)𝜓) | 
| 43 | 42 | expcom 116 | 
. . . . 5
⊢ (𝑁 ∈
(ℤ≥‘𝑀) → (𝜑 → DECID ∃𝑛 ∈ (𝑀...𝑀)𝜓)) | 
| 44 |   | simpr 110 | 
. . . . . . . . . 10
⊢ (((𝑦 ∈ (𝑀..^𝑁) ∧ 𝜑) ∧ DECID ∃𝑛 ∈ (𝑀...𝑦)𝜓) → DECID ∃𝑛 ∈ (𝑀...𝑦)𝜓) | 
| 45 |   | fzofzp1 10303 | 
. . . . . . . . . . . . 13
⊢ (𝑦 ∈ (𝑀..^𝑁) → (𝑦 + 1) ∈ (𝑀...𝑁)) | 
| 46 | 45 | ad2antrr 488 | 
. . . . . . . . . . . 12
⊢ (((𝑦 ∈ (𝑀..^𝑁) ∧ 𝜑) ∧ DECID ∃𝑛 ∈ (𝑀...𝑦)𝜓) → (𝑦 + 1) ∈ (𝑀...𝑁)) | 
| 47 | 27 | ad2antlr 489 | 
. . . . . . . . . . . 12
⊢ (((𝑦 ∈ (𝑀..^𝑁) ∧ 𝜑) ∧ DECID ∃𝑛 ∈ (𝑀...𝑦)𝜓) → ∀𝑛 ∈ (𝑀...𝑁)DECID 𝜓) | 
| 48 |   | nfsbc1v 3008 | 
. . . . . . . . . . . . . 14
⊢
Ⅎ𝑛[(𝑦 + 1) / 𝑛]𝜓 | 
| 49 | 48 | nfdc 1673 | 
. . . . . . . . . . . . 13
⊢
Ⅎ𝑛DECID [(𝑦 + 1) / 𝑛]𝜓 | 
| 50 |   | sbceq1a 2999 | 
. . . . . . . . . . . . . 14
⊢ (𝑛 = (𝑦 + 1) → (𝜓 ↔ [(𝑦 + 1) / 𝑛]𝜓)) | 
| 51 | 50 | dcbid 839 | 
. . . . . . . . . . . . 13
⊢ (𝑛 = (𝑦 + 1) → (DECID 𝜓 ↔ DECID
[(𝑦 + 1) / 𝑛]𝜓)) | 
| 52 | 49, 51 | rspc 2862 | 
. . . . . . . . . . . 12
⊢ ((𝑦 + 1) ∈ (𝑀...𝑁) → (∀𝑛 ∈ (𝑀...𝑁)DECID 𝜓 → DECID [(𝑦 + 1) / 𝑛]𝜓)) | 
| 53 | 46, 47, 52 | sylc 62 | 
. . . . . . . . . . 11
⊢ (((𝑦 ∈ (𝑀..^𝑁) ∧ 𝜑) ∧ DECID ∃𝑛 ∈ (𝑀...𝑦)𝜓) → DECID [(𝑦 + 1) / 𝑛]𝜓) | 
| 54 |   | rexsns 3661 | 
. . . . . . . . . . . 12
⊢
(∃𝑛 ∈
{(𝑦 + 1)}𝜓 ↔ [(𝑦 + 1) / 𝑛]𝜓) | 
| 55 | 54 | dcbii 841 | 
. . . . . . . . . . 11
⊢
(DECID ∃𝑛 ∈ {(𝑦 + 1)}𝜓 ↔ DECID [(𝑦 + 1) / 𝑛]𝜓) | 
| 56 | 53, 55 | sylibr 134 | 
. . . . . . . . . 10
⊢ (((𝑦 ∈ (𝑀..^𝑁) ∧ 𝜑) ∧ DECID ∃𝑛 ∈ (𝑀...𝑦)𝜓) → DECID ∃𝑛 ∈ {(𝑦 + 1)}𝜓) | 
| 57 |   | dcor 937 | 
. . . . . . . . . 10
⊢
(DECID ∃𝑛 ∈ (𝑀...𝑦)𝜓 → (DECID ∃𝑛 ∈ {(𝑦 + 1)}𝜓 → DECID (∃𝑛 ∈ (𝑀...𝑦)𝜓 ∨ ∃𝑛 ∈ {(𝑦 + 1)}𝜓))) | 
| 58 | 44, 56, 57 | sylc 62 | 
. . . . . . . . 9
⊢ (((𝑦 ∈ (𝑀..^𝑁) ∧ 𝜑) ∧ DECID ∃𝑛 ∈ (𝑀...𝑦)𝜓) → DECID (∃𝑛 ∈ (𝑀...𝑦)𝜓 ∨ ∃𝑛 ∈ {(𝑦 + 1)}𝜓)) | 
| 59 |   | rexun 3343 | 
. . . . . . . . . 10
⊢
(∃𝑛 ∈
((𝑀...𝑦) ∪ {(𝑦 + 1)})𝜓 ↔ (∃𝑛 ∈ (𝑀...𝑦)𝜓 ∨ ∃𝑛 ∈ {(𝑦 + 1)}𝜓)) | 
| 60 | 59 | dcbii 841 | 
. . . . . . . . 9
⊢
(DECID ∃𝑛 ∈ ((𝑀...𝑦) ∪ {(𝑦 + 1)})𝜓 ↔ DECID (∃𝑛 ∈ (𝑀...𝑦)𝜓 ∨ ∃𝑛 ∈ {(𝑦 + 1)}𝜓)) | 
| 61 | 58, 60 | sylibr 134 | 
. . . . . . . 8
⊢ (((𝑦 ∈ (𝑀..^𝑁) ∧ 𝜑) ∧ DECID ∃𝑛 ∈ (𝑀...𝑦)𝜓) → DECID ∃𝑛 ∈ ((𝑀...𝑦) ∪ {(𝑦 + 1)})𝜓) | 
| 62 |   | elfzouz 10226 | 
. . . . . . . . . . . 12
⊢ (𝑦 ∈ (𝑀..^𝑁) → 𝑦 ∈ (ℤ≥‘𝑀)) | 
| 63 | 62 | ad2antrr 488 | 
. . . . . . . . . . 11
⊢ (((𝑦 ∈ (𝑀..^𝑁) ∧ 𝜑) ∧ DECID ∃𝑛 ∈ (𝑀...𝑦)𝜓) → 𝑦 ∈ (ℤ≥‘𝑀)) | 
| 64 |   | fzsuc 10144 | 
. . . . . . . . . . 11
⊢ (𝑦 ∈
(ℤ≥‘𝑀) → (𝑀...(𝑦 + 1)) = ((𝑀...𝑦) ∪ {(𝑦 + 1)})) | 
| 65 | 63, 64 | syl 14 | 
. . . . . . . . . 10
⊢ (((𝑦 ∈ (𝑀..^𝑁) ∧ 𝜑) ∧ DECID ∃𝑛 ∈ (𝑀...𝑦)𝜓) → (𝑀...(𝑦 + 1)) = ((𝑀...𝑦) ∪ {(𝑦 + 1)})) | 
| 66 | 65 | rexeqdv 2700 | 
. . . . . . . . 9
⊢ (((𝑦 ∈ (𝑀..^𝑁) ∧ 𝜑) ∧ DECID ∃𝑛 ∈ (𝑀...𝑦)𝜓) → (∃𝑛 ∈ (𝑀...(𝑦 + 1))𝜓 ↔ ∃𝑛 ∈ ((𝑀...𝑦) ∪ {(𝑦 + 1)})𝜓)) | 
| 67 | 66 | dcbid 839 | 
. . . . . . . 8
⊢ (((𝑦 ∈ (𝑀..^𝑁) ∧ 𝜑) ∧ DECID ∃𝑛 ∈ (𝑀...𝑦)𝜓) → (DECID ∃𝑛 ∈ (𝑀...(𝑦 + 1))𝜓 ↔ DECID ∃𝑛 ∈ ((𝑀...𝑦) ∪ {(𝑦 + 1)})𝜓)) | 
| 68 | 61, 67 | mpbird 167 | 
. . . . . . 7
⊢ (((𝑦 ∈ (𝑀..^𝑁) ∧ 𝜑) ∧ DECID ∃𝑛 ∈ (𝑀...𝑦)𝜓) → DECID ∃𝑛 ∈ (𝑀...(𝑦 + 1))𝜓) | 
| 69 | 68 | exp31 364 | 
. . . . . 6
⊢ (𝑦 ∈ (𝑀..^𝑁) → (𝜑 → (DECID ∃𝑛 ∈ (𝑀...𝑦)𝜓 → DECID ∃𝑛 ∈ (𝑀...(𝑦 + 1))𝜓))) | 
| 70 | 69 | a2d 26 | 
. . . . 5
⊢ (𝑦 ∈ (𝑀..^𝑁) → ((𝜑 → DECID ∃𝑛 ∈ (𝑀...𝑦)𝜓) → (𝜑 → DECID ∃𝑛 ∈ (𝑀...(𝑦 + 1))𝜓))) | 
| 71 | 11, 15, 19, 23, 43, 70 | fzind2 10315 | 
. . . 4
⊢ (𝑁 ∈ (𝑀...𝑁) → (𝜑 → DECID ∃𝑛 ∈ (𝑀...𝑁)𝜓)) | 
| 72 | 7, 71 | syl 14 | 
. . 3
⊢ (𝑁 ∈
(ℤ≥‘𝑀) → (𝜑 → DECID ∃𝑛 ∈ (𝑀...𝑁)𝜓)) | 
| 73 | 5, 6, 72 | sylc 62 | 
. 2
⊢ ((𝜑 ∧ 𝑀 ≤ 𝑁) → DECID ∃𝑛 ∈ (𝑀...𝑁)𝜓) | 
| 74 |   | rex0 3468 | 
. . . . 5
⊢  ¬
∃𝑛 ∈ ∅
𝜓 | 
| 75 |   | zltnle 9372 | 
. . . . . . . . 9
⊢ ((𝑁 ∈ ℤ ∧ 𝑀 ∈ ℤ) → (𝑁 < 𝑀 ↔ ¬ 𝑀 ≤ 𝑁)) | 
| 76 | 2, 1, 75 | syl2anc 411 | 
. . . . . . . 8
⊢ (𝜑 → (𝑁 < 𝑀 ↔ ¬ 𝑀 ≤ 𝑁)) | 
| 77 | 76 | biimpar 297 | 
. . . . . . 7
⊢ ((𝜑 ∧ ¬ 𝑀 ≤ 𝑁) → 𝑁 < 𝑀) | 
| 78 |   | fzn 10117 | 
. . . . . . . . 9
⊢ ((𝑀 ∈ ℤ ∧ 𝑁 ∈ ℤ) → (𝑁 < 𝑀 ↔ (𝑀...𝑁) = ∅)) | 
| 79 | 1, 2, 78 | syl2anc 411 | 
. . . . . . . 8
⊢ (𝜑 → (𝑁 < 𝑀 ↔ (𝑀...𝑁) = ∅)) | 
| 80 | 79 | adantr 276 | 
. . . . . . 7
⊢ ((𝜑 ∧ ¬ 𝑀 ≤ 𝑁) → (𝑁 < 𝑀 ↔ (𝑀...𝑁) = ∅)) | 
| 81 | 77, 80 | mpbid 147 | 
. . . . . 6
⊢ ((𝜑 ∧ ¬ 𝑀 ≤ 𝑁) → (𝑀...𝑁) = ∅) | 
| 82 | 81 | rexeqdv 2700 | 
. . . . 5
⊢ ((𝜑 ∧ ¬ 𝑀 ≤ 𝑁) → (∃𝑛 ∈ (𝑀...𝑁)𝜓 ↔ ∃𝑛 ∈ ∅ 𝜓)) | 
| 83 | 74, 82 | mtbiri 676 | 
. . . 4
⊢ ((𝜑 ∧ ¬ 𝑀 ≤ 𝑁) → ¬ ∃𝑛 ∈ (𝑀...𝑁)𝜓) | 
| 84 | 83 | olcd 735 | 
. . 3
⊢ ((𝜑 ∧ ¬ 𝑀 ≤ 𝑁) → (∃𝑛 ∈ (𝑀...𝑁)𝜓 ∨ ¬ ∃𝑛 ∈ (𝑀...𝑁)𝜓)) | 
| 85 |   | df-dc 836 | 
. . 3
⊢
(DECID ∃𝑛 ∈ (𝑀...𝑁)𝜓 ↔ (∃𝑛 ∈ (𝑀...𝑁)𝜓 ∨ ¬ ∃𝑛 ∈ (𝑀...𝑁)𝜓)) | 
| 86 | 84, 85 | sylibr 134 | 
. 2
⊢ ((𝜑 ∧ ¬ 𝑀 ≤ 𝑁) → DECID ∃𝑛 ∈ (𝑀...𝑁)𝜓) | 
| 87 |   | zdcle 9402 | 
. . . 4
⊢ ((𝑀 ∈ ℤ ∧ 𝑁 ∈ ℤ) →
DECID 𝑀 ≤
𝑁) | 
| 88 |   | exmiddc 837 | 
. . . 4
⊢
(DECID 𝑀 ≤ 𝑁 → (𝑀 ≤ 𝑁 ∨ ¬ 𝑀 ≤ 𝑁)) | 
| 89 | 87, 88 | syl 14 | 
. . 3
⊢ ((𝑀 ∈ ℤ ∧ 𝑁 ∈ ℤ) → (𝑀 ≤ 𝑁 ∨ ¬ 𝑀 ≤ 𝑁)) | 
| 90 | 1, 2, 89 | syl2anc 411 | 
. 2
⊢ (𝜑 → (𝑀 ≤ 𝑁 ∨ ¬ 𝑀 ≤ 𝑁)) | 
| 91 | 73, 86, 90 | mpjaodan 799 | 
1
⊢ (𝜑 → DECID
∃𝑛 ∈ (𝑀...𝑁)𝜓) |