Metamath Proof Explorer


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
8 0re 0
9 7 8 ifcli if X A 1 0
10 9 a1i O V A O X O if X A 1 0
11 2 5 6 10 fvmptd O V A O X O 𝟙 O A X = if X A 1 0