Definition df-exp 10648

Description: Define exponentiation to nonnegative integer powers. For example, ( 5 ^ 2 ) = 2 5 (see ex-exp 15457).

This definition is not meant to be used directly; instead, exp0 10652 and expp1 10655 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 (see 0exp0e1 10653).

4-Jun-2014: The definition was extended to include negative integer exponents. For example, ( -u 3 ^ -u 2 ) = ( 1 / 9 ) (ex-exp 15457). The case x = 0 , y < 0 gives the value ( 1 / 0 ), so we will avoid this case in our theorems. (Contributed by Raph Levien, 20-May-2004.) (Revised by NM, 15-Oct-2004.)

Assertion

Ref	Expression
df-exp	|- ^ = ( x e. CC , y e. ZZ |-> if ( y = 0 , 1 , if ( 0 < y , ( seq 1 ( x. , ( NN X. { x } ) ) ` y ) , ( 1 / ( seq 1 ( x. , ( NN X. { x } ) ) ` -u y ) ) ) ) )

Distinct variable group:   x, y

Detailed syntax breakdown of Definition df-exp

Step	Hyp	Ref	Expression
1		cexp 10647	. 2 class ^
2		vx	. . 3 setvar x
3		vy	. . 3 setvar y
4		cc 7894	. . 3 class CC
5		cz 9343	. . 3 class ZZ
6	3	cv 1363	. . . . 5 class y
7		cc0 7896	. . . . 5 class 0
8	6, 7	wceq 1364	. . . 4 wff y = 0
9		c1 7897	. . . 4 class 1
10		clt 8078	. . . . . 6 class <
11	7, 6, 10	wbr 4034	. . . . 5 wff 0 < y
12		cmul 7901	. . . . . . 7 class x.
13		cn 9007	. . . . . . . 8 class NN
14	2	cv 1363	. . . . . . . . 9 class x
15	14	csn 3623	. . . . . . . 8 class { x }
16	13, 15	cxp 4662	. . . . . . 7 class ( NN X. { x } )
17	12, 16, 9	cseq 10556	. . . . . 6 class seq 1 ( x. , ( NN X. { x } ) )
18	6, 17	cfv 5259	. . . . 5 class ( seq 1 ( x. , ( NN X. { x } ) ) ` y )
19	6	cneg 8215	. . . . . . 7 class -u y
20	19, 17	cfv 5259	. . . . . 6 class ( seq 1 ( x. , ( NN X. { x } ) ) ` -u y )
21		cdiv 8716	. . . . . 6 class /
22	9, 20, 21	co 5925	. . . . 5 class ( 1 / ( seq 1 ( x. , ( NN X. { x } ) ) ` -u y ) )
23	11, 18, 22	cif 3562	. . . 4 class if ( 0 < y , ( seq 1 ( x. , ( NN X. { x } ) ) ` y ) , ( 1 / ( seq 1 ( x. , ( NN X. { x } ) ) ` -u y ) ) )
24	8, 9, 23	cif 3562	. . 3 class if ( y = 0 , 1 , if ( 0 < y , ( seq 1 ( x. , ( NN X. { x } ) ) ` y ) , ( 1 / ( seq 1 ( x. , ( NN X. { x } ) ) ` -u y ) ) ) )
25	2, 3, 4, 5, 24	cmpo 5927	. 2 class ( x e. CC , y e. ZZ |-> if ( y = 0 , 1 , if ( 0 < y , ( seq 1 ( x. , ( NN X. { x } ) ) ` y ) , ( 1 / ( seq 1 ( x. , ( NN X. { x } ) ) ` -u y ) ) ) ) )
26	1, 25	wceq 1364	1 wff ^ = ( x e. CC , y e. ZZ |-> if ( y = 0 , 1 , if ( 0 < y , ( seq 1 ( x. , ( NN X. { x } ) ) ` y ) , ( 1 / ( seq 1 ( x. , ( NN X. { x } ) ) ` -u y ) ) ) ) )

This definition is referenced by:  exp3val  10650