let X be set ; :: thesis: for L1, L2 being List of X
for O, O1, O2, O3 being Operation of X st O1 c= O2 & L1 c= L2 & O c= O3 holds
L1 WHEREge (O,O2) c= L2 WHEREge (O3,O1)

let L1, L2 be List of X; :: thesis: for O, O1, O2, O3 being Operation of X st O1 c= O2 & L1 c= L2 & O c= O3 holds
L1 WHEREge (O,O2) c= L2 WHEREge (O3,O1)

let O, O1, O2, O3 be Operation of X; :: thesis: ( O1 c= O2 & L1 c= L2 & O c= O3 implies L1 WHEREge (O,O2) c= L2 WHEREge (O3,O1) )
assume A1: ( O1 c= O2 & L1 c= L2 & O c= O3 ) ; :: thesis: L1 WHEREge (O,O2) c= L2 WHEREge (O3,O1)
let z be object ; :: according to TARSKI:def 3 :: thesis: ( not z in L1 WHEREge (O,O2) or z in L2 WHEREge (O3,O1) )
assume z in L1 WHEREge (O,O2) ; :: thesis: z in L2 WHEREge (O3,O1)
then consider x being Element of X such that
A2: ( z = x & card (x . O2) c= card (x . O) & x in L1 ) ;
A3: ( card (x . O1) c= card (x . O2) & card (x . O) c= card (x . O3) ) by ;
then card (x . O1) c= card (x . O) by A2;
then card (x . O1) c= card (x . O3) by A3;
hence z in L2 WHEREge (O3,O1) by A2, A1; :: thesis: verum