Metamath Proof Explorer


Theorem cardpred

Description: The cardinality function preserves predecessors. (Contributed by BTernaryTau, 18-Jul-2024)

Ref Expression
Assertion cardpred A dom card B dom card Pred E card A card B = card Pred A B

Proof

Step Hyp Ref Expression
1 cardf2 card : x | y On y x On
2 ffun card : x | y On y x On Fun card
3 2 funfnd card : x | y On y x On card Fn dom card
4 1 3 mp1i A dom card B dom card card Fn dom card
5 fvex card y V
6 5 epeli card x E card y card x card y
7 cardsdom2 x dom card y dom card card x card y x y
8 6 7 bitr2id x dom card y dom card x y card x E card y
9 8 rgen2 x dom card y dom card x y card x E card y
10 9 a1i A dom card B dom card x dom card y dom card x y card x E card y
11 simpl A dom card B dom card A dom card
12 simpr A dom card B dom card B dom card
13 4 10 11 12 fnrelpredd A dom card B dom card Pred E card A card B = card Pred A B