Definition df-fl 10634

Description: Define the floor (greatest integer less than or equal to) function. See flval 10636 for its value, flqlelt 10640 for its basic property, and flqcl 10637 for its closure. For example, ( |_ ` ( 3 / 2 ) ) = 1 while ( |_ ` -u ( 3 / 2 ) ) = -u 2 (ex-fl 16510).

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 10632	. 2 class |_
2		vx	. . 3 setvar x
3		cr 8128	. . 3 class RR
4		vy	. . . . . . 7 setvar y
5	4	cv 1397	. . . . . 6 class y
6	2	cv 1397	. . . . . 6 class x
7		cle 8311	. . . . . 6 class <_
8	5, 6, 7	wbr 4111	. . . . 5 wff y <_ x
9		c1 8130	. . . . . . 7 class 1
10		caddc 8132	. . . . . . 7 class +
11	5, 9, 10	co 6052	. . . . . 6 class ( y + 1 )
12		clt 8310	. . . . . 6 class <
13	6, 11, 12	wbr 4111	. . . . 5 wff x < ( y + 1 )
14	8, 13	wa 104	. . . 4 wff ( y <_ x /\ x < ( y + 1 ) )
15		cz 9579	. . . 4 class ZZ
16	14, 4, 15	crio 6004	. . 3 class ( iota_ y e. ZZ ( y <_ x /\ x < ( y + 1 ) ) )
17	2, 3, 16	cmpt 4173	. 2 class ( x e. RR |-> ( iota_ y e. ZZ ( y <_ x /\ x < ( y + 1 ) ) ) )
18	1, 17	wceq 1398	1 wff |_ = ( x e. RR |-> ( iota_ y e. ZZ ( y <_ x /\ x < ( y + 1 ) ) ) )

This definition is referenced by:  flval  10636