Description: Commutative/associative law that swaps the first two factors in a triple product. (Contributed by NM, 11-May-1999) (Proof shortened by Andrew Salmon, 19-Nov-2011)
Ref | Expression | ||
---|---|---|---|
Hypotheses | mul.1 | |
|
mul.2 | |
||
mul.3 | |
||
Assertion | mul12i | |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | mul.1 | |
|
2 | mul.2 | |
|
3 | mul.3 | |
|
4 | mul12 | |
|
5 | 1 2 3 4 | mp3an | |