Metamath Proof Explorer


Theorem ssinss1OLD

Description: Obsolete version of ssinss1 as of 10-Jun-2026. (Contributed by NM, 14-Sep-1999) (Proof modification is discouraged.) (New usage is discouraged.)

Ref Expression
Assertion ssinss1OLD
|- ( A C_ C -> ( A i^i B ) C_ C )

Proof

Step Hyp Ref Expression
1 inss1
 |-  ( A i^i B ) C_ A
2 sstr2
 |-  ( ( A i^i B ) C_ A -> ( A C_ C -> ( A i^i B ) C_ C ) )
3 1 2 ax-mp
 |-  ( A C_ C -> ( A i^i B ) C_ C )