for U being non empty set
for S being Language
for phi being wff string of S
for I1, I2 being Element of U -InterpretersOf S st I1 | ((rng phi) /\ (OwnSymbolsOf S)) = I2 | ((rng phi) /\ (OwnSymbolsOf S)) holds
I1 -TruthEval phi = I2 -TruthEval phi