theorem nfsb1 {x: nat} (a: nat) (b: wff x): $ F/ x [a / x] b $;
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | nfv | F/ x y = a |
|
2 | nfal1 | F/ x A. x (x = y -> b) |
|
3 | 1, 2 | nfim | F/ x y = a -> A. x (x = y -> b) |
4 | 3 | nfal | F/ x A. y (y = a -> A. x (x = y -> b)) |
5 | 4 | conv sb | F/ x [a / x] b |