Database
SUPPLEMENTARY MATERIAL (USERS' MATHBOXES)
Mathbox for Thierry Arnoux
Real and complex functions
Indicator Functions
indfval
Next ⟩
ind1
Metamath Proof Explorer
Ascii
Unicode
Theorem
indfval
Description:
Value of the indicator function.
(Contributed by
Thierry Arnoux
, 13-Aug-2017)
Ref
Expression
Assertion
indfval
⊢
O
∈
V
∧
A
⊆
O
∧
X
∈
O
→
𝟙
O
⁡
A
⁡
X
=
if
X
∈
A
1
0
Proof
Step
Hyp
Ref
Expression
1
indval
⊢
O
∈
V
∧
A
⊆
O
→
𝟙
O
⁡
A
=
x
∈
O
⟼
if
x
∈
A
1
0
2
1
3adant3
⊢
O
∈
V
∧
A
⊆
O
∧
X
∈
O
→
𝟙
O
⁡
A
=
x
∈
O
⟼
if
x
∈
A
1
0
3
simpr
⊢
O
∈
V
∧
A
⊆
O
∧
X
∈
O
∧
x
=
X
→
x
=
X
4
3
eleq1d
⊢
O
∈
V
∧
A
⊆
O
∧
X
∈
O
∧
x
=
X
→
x
∈
A
↔
X
∈
A
5
4
ifbid
⊢
O
∈
V
∧
A
⊆
O
∧
X
∈
O
∧
x
=
X
→
if
x
∈
A
1
0
=
if
X
∈
A
1
0
6
simp3
⊢
O
∈
V
∧
A
⊆
O
∧
X
∈
O
→
X
∈
O
7
1re
⊢
1
∈
ℝ
8
0re
⊢
0
∈
ℝ
9
7
8
ifcli
⊢
if
X
∈
A
1
0
∈
ℝ
10
9
a1i
⊢
O
∈
V
∧
A
⊆
O
∧
X
∈
O
→
if
X
∈
A
1
0
∈
ℝ
11
2
5
6
10
fvmptd
⊢
O
∈
V
∧
A
⊆
O
∧
X
∈
O
→
𝟙
O
⁡
A
⁡
X
=
if
X
∈
A
1
0