Description: A composition law for class substitution. Importantly, x may occur free in the class expression substituted for A . (Contributed by NM, 5-Sep-2004) (Proof shortened by Andrew Salmon, 8-Jun-2011)
Ref | Expression | ||
---|---|---|---|
Hypothesis | sbcco2.1 | |
|
Assertion | sbcco2 | |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | sbcco2.1 | |
|
2 | sbsbc | |
|
3 | 1 | equcoms | |
4 | dfsbcq | |
|
5 | 4 | bicomd | |
6 | 3 5 | syl | |
7 | 6 | sbievw | |
8 | 2 7 | bitr3i | |