 where \(\bsigma[\Gamma]\) is the set of the formulas obtained by applying the substitution \(\sigma\) to the formulas in \(\Gamma\). The consequence relations on the set of formulas of a language that satisfy this property are called structural and also substitution-invariant in the literature. They were considered for the first time in Łoś &amp; Suszko 1958. Tarski only explicitly considered closed sets also closed under substitution instances for some consequence relations; he never considered (at least explicitly) the substitution invariance condition for consequence relations.