let S be non empty partial quasi_total non-empty Group-like invariant TRSStr ; :: thesis: for a, b being Element of S st S is (R9) holds
((a ") ") * b =*=> a * b
let a, b be Element of S; :: thesis: ( S is (R9) implies ((a ") ") * b =*=> a * b )
assume S is (R9) ; :: thesis: ((a ") ") * b =*=> a * b
then (a ") " ==> a ;
hence ((a ") ") * b =*=> a * b by Th2, ThI2; :: thesis: verum