Definition df-iexp 9476

Description: Define exponentiation to nonnegative integer powers. This definition is not meant to be used directly; instead, exp0 9480 and expp1 9483 provide the standard recursive definition. The up-arrow notation is used by Donald Knuth for iterated exponentiation (Science 194, 1235-1242, 1976) and is convenient for us since we don't have superscripts. 10-Jun-2005: The definition was extended to include zero exponents, so that 0↑0 = 1 per the convention of Definition 10-4.1 of [Gleason] p. 134. 4-Jun-2014: The definition was extended to include negative integer exponents. The case 𝑥 = 0, 𝑦 < 0 gives the value (1 / 0), so we will avoid this case in our theorems. (Contributed by Jim Kingdon, 7-Jun-2020.)

Assertion

Ref	Expression
df-iexp	⊢ ↑ = (𝑥 ∈ ℂ, 𝑦 ∈ ℤ ↦ if(𝑦 = 0, 1, if(0 < 𝑦, (seq1( · , (ℕ × {𝑥}), ℂ)‘𝑦), (1 / (seq1( · , (ℕ × {𝑥}), ℂ)‘-𝑦)))))

Distinct variable group:   𝑥,𝑦

Detailed syntax breakdown of Definition df-iexp

Step	Hyp	Ref	Expression
1		cexp 9475	. 2 class ↑
2		vx	. . 3 setvar 𝑥
3		vy	. . 3 setvar 𝑦
4		cc 6979	. . 3 class ℂ
5		cz 8351	. . 3 class ℤ
6	3	cv 1283	. . . . 5 class 𝑦
7		cc0 6981	. . . . 5 class 0
8	6, 7	wceq 1284	. . . 4 wff 𝑦 = 0
9		c1 6982	. . . 4 class 1
10		clt 7153	. . . . . 6 class <
11	7, 6, 10	wbr 3785	. . . . 5 wff 0 < 𝑦
12		cmul 6986	. . . . . . 7 class ·
13		cn 8039	. . . . . . . 8 class ℕ
14	2	cv 1283	. . . . . . . . 9 class 𝑥
15	14	csn 3398	. . . . . . . 8 class {𝑥}
16	13, 15	cxp 4361	. . . . . . 7 class (ℕ × {𝑥})
17	12, 4, 16, 9	cseq 9431	. . . . . 6 class seq1( · , (ℕ × {𝑥}), ℂ)
18	6, 17	cfv 4922	. . . . 5 class (seq1( · , (ℕ × {𝑥}), ℂ)‘𝑦)
19	6	cneg 7280	. . . . . . 7 class -𝑦
20	19, 17	cfv 4922	. . . . . 6 class (seq1( · , (ℕ × {𝑥}), ℂ)‘-𝑦)
21		cdiv 7760	. . . . . 6 class /
22	9, 20, 21	co 5532	. . . . 5 class (1 / (seq1( · , (ℕ × {𝑥}), ℂ)‘-𝑦))
23	11, 18, 22	cif 3351	. . . 4 class if(0 < 𝑦, (seq1( · , (ℕ × {𝑥}), ℂ)‘𝑦), (1 / (seq1( · , (ℕ × {𝑥}), ℂ)‘-𝑦)))
24	8, 9, 23	cif 3351	. . 3 class if(𝑦 = 0, 1, if(0 < 𝑦, (seq1( · , (ℕ × {𝑥}), ℂ)‘𝑦), (1 / (seq1( · , (ℕ × {𝑥}), ℂ)‘-𝑦))))
25	2, 3, 4, 5, 24	cmpt2 5534	. 2 class (𝑥 ∈ ℂ, 𝑦 ∈ ℤ ↦ if(𝑦 = 0, 1, if(0 < 𝑦, (seq1( · , (ℕ × {𝑥}), ℂ)‘𝑦), (1 / (seq1( · , (ℕ × {𝑥}), ℂ)‘-𝑦)))))
26	1, 25	wceq 1284	1 wff ↑ = (𝑥 ∈ ℂ, 𝑦 ∈ ℤ ↦ if(𝑦 = 0, 1, if(0 < 𝑦, (seq1( · , (ℕ × {𝑥}), ℂ)‘𝑦), (1 / (seq1( · , (ℕ × {𝑥}), ℂ)‘-𝑦)))))

This definition is referenced by:  expival  9478