theorem for I being Element of U-InterpretersOf S holds
I-TruthEval phi=1 iff {phi} is I-satisfied
proof
let I be Element of U-InterpretersOf S;
thus I-TruthEval phi=1 implies {phi} is I-satisfied by TARSKI:def 1;
assume {phi} is I-satisfied; then reconsider X={phi} as I-satisfied set;
phi in X by TARSKI:def 1; hence I-TruthEval phi=1 by Def41;
end;
