-
Notifications
You must be signed in to change notification settings - Fork 1
/
Funcion_no_acotada_inferiormente.lean
51 lines (44 loc) · 1.18 KB
/
Funcion_no_acotada_inferiormente.lean
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
-- ---------------------------------------------------------------------
-- Ejercicio. Demostrar que si f es una función de ℝ en ℝ tal que
-- para cada a, existe un x tal que f x < a, entonces f no tiene cota
-- inferior.
-- ----------------------------------------------------------------------
import data.real.basic
def fn_ub (f : ℝ → ℝ) (a : ℝ) : Prop := ∀ x, f x ≤ a
def fn_lb (f : ℝ → ℝ) (a : ℝ) : Prop := ∀ x, a ≤ f x
def fn_has_ub (f : ℝ → ℝ) := ∃ a, fn_ub f a
def fn_has_lb (f : ℝ → ℝ) := ∃ a, fn_lb f a
variable f : ℝ → ℝ
example
(h : ∀ a, ∃ x, f x < a)
: ¬ fn_has_lb f :=
begin
intros fnlb,
cases fnlb with a fnlba,
cases h a with x hx,
have : a ≤ f x,
from fnlba x,
linarith,
end
-- Prueba
-- ------
-- f : ℝ → ℝ,
-- h : ∀ (a : ℝ), ∃ (x : ℝ), f x < a
-- ⊢ ¬fn_has_lb f
-- >> intros fnlb,
-- fnlb : fn_has_lb f
-- ⊢ false
-- >> cases fnlb with a fnlba,
-- a : ℝ,
-- fnlba : fn_lb f a
-- ⊢ false
-- >> cases h a with x hx,
-- x : ℝ,
-- hx : f x < a
-- ⊢ false
-- >> have : a ≤ f x,
-- >> from fnlba x,
-- this : a ≤ f x
-- ⊢ false
-- >> linarith,
-- no goals