Definition df-fl 10529

Description: Define the floor (greatest integer less than or equal to) function. See flval 10531 for its value, flqlelt 10535 for its basic property, and flqcl 10532 for its closure. For example, ( |_ ` ( 3 / 2 ) ) = 1 while ( |_ ` -u ( 3 / 2 ) ) = -u 2 (ex-fl 16321).

Although we define this on real numbers so that notations are similar to the Metamath Proof Explorer, in the absence of excluded middle few theorems will be possible for all real numbers. Imagine a real number which is around 2.99995 or 3.00001 . In order to determine whether its floor is 2 or 3, it would be necessary to compute the number to arbitrary precision.

The term "floor" was coined by Ken Iverson. He also invented a mathematical notation for floor, consisting of an L-shaped left bracket and its reflection as a right bracket. In APL, the left-bracket alone is used, and we borrow this idea. (Thanks to Paul Chapman for this information.) (Contributed by NM, 14-Nov-2004.)

Assertion

Ref	Expression
df-fl	|- |_ = ( x e. RR |-> ( iota_ y e. ZZ ( y <_ x /\ x < ( y + 1 ) ) ) )

Distinct variable group:   x, y

Detailed syntax breakdown of Definition df-fl

Step	Hyp	Ref	Expression
1		cfl 10527	. 2 class |_
2		vx	. . 3 setvar x
3		cr 8030	. . 3 class RR
4		vy	. . . . . . 7 setvar y
5	4	cv 1396	. . . . . 6 class y
6	2	cv 1396	. . . . . 6 class x
7		cle 8214	. . . . . 6 class <_
8	5, 6, 7	wbr 4088	. . . . 5 wff y <_ x
9		c1 8032	. . . . . . 7 class 1
10		caddc 8034	. . . . . . 7 class +
11	5, 9, 10	co 6017	. . . . . 6 class ( y + 1 )
12		clt 8213	. . . . . 6 class <
13	6, 11, 12	wbr 4088	. . . . 5 wff x < ( y + 1 )
14	8, 13	wa 104	. . . 4 wff ( y <_ x /\ x < ( y + 1 ) )
15		cz 9478	. . . 4 class ZZ
16	14, 4, 15	crio 5969	. . 3 class ( iota_ y e. ZZ ( y <_ x /\ x < ( y + 1 ) ) )
17	2, 3, 16	cmpt 4150	. 2 class ( x e. RR |-> ( iota_ y e. ZZ ( y <_ x /\ x < ( y + 1 ) ) ) )
18	1, 17	wceq 1397	1 wff |_ = ( x e. RR |-> ( iota_ y e. ZZ ( y <_ x /\ x < ( y + 1 ) ) ) )

This definition is referenced by:  flval  10531