Metamath Proof Explorer


Theorem hashbcval

Description: Value of the "binomial set", the set of all N -element subsets of A . (Contributed by Mario Carneiro, 20-Apr-2015)

Ref Expression
Hypothesis ramval.c
|- C = ( a e. _V , i e. NN0 |-> { b e. ~P a | ( # ` b ) = i } )
Assertion hashbcval
|- ( ( A e. V /\ N e. NN0 ) -> ( A C N ) = { x e. ~P A | ( # ` x ) = N } )

Proof

Step Hyp Ref Expression
1 ramval.c
 |-  C = ( a e. _V , i e. NN0 |-> { b e. ~P a | ( # ` b ) = i } )
2 elex
 |-  ( A e. V -> A e. _V )
3 pwexg
 |-  ( A e. _V -> ~P A e. _V )
4 3 adantr
 |-  ( ( A e. _V /\ N e. NN0 ) -> ~P A e. _V )
5 rabexg
 |-  ( ~P A e. _V -> { x e. ~P A | ( # ` x ) = N } e. _V )
6 4 5 syl
 |-  ( ( A e. _V /\ N e. NN0 ) -> { x e. ~P A | ( # ` x ) = N } e. _V )
7 fveqeq2
 |-  ( b = x -> ( ( # ` b ) = i <-> ( # ` x ) = i ) )
8 7 cbvrabv
 |-  { b e. ~P a | ( # ` b ) = i } = { x e. ~P a | ( # ` x ) = i }
9 simpl
 |-  ( ( a = A /\ i = N ) -> a = A )
10 9 pweqd
 |-  ( ( a = A /\ i = N ) -> ~P a = ~P A )
11 simpr
 |-  ( ( a = A /\ i = N ) -> i = N )
12 11 eqeq2d
 |-  ( ( a = A /\ i = N ) -> ( ( # ` x ) = i <-> ( # ` x ) = N ) )
13 10 12 rabeqbidv
 |-  ( ( a = A /\ i = N ) -> { x e. ~P a | ( # ` x ) = i } = { x e. ~P A | ( # ` x ) = N } )
14 8 13 syl5eq
 |-  ( ( a = A /\ i = N ) -> { b e. ~P a | ( # ` b ) = i } = { x e. ~P A | ( # ` x ) = N } )
15 14 1 ovmpoga
 |-  ( ( A e. _V /\ N e. NN0 /\ { x e. ~P A | ( # ` x ) = N } e. _V ) -> ( A C N ) = { x e. ~P A | ( # ` x ) = N } )
16 6 15 mpd3an3
 |-  ( ( A e. _V /\ N e. NN0 ) -> ( A C N ) = { x e. ~P A | ( # ` x ) = N } )
17 2 16 sylan
 |-  ( ( A e. V /\ N e. NN0 ) -> ( A C N ) = { x e. ~P A | ( # ` x ) = N } )