21. There are no free variables to replace. 22. As " p " is a free variable in the whole expression, the parameter may be dropped. 23. Step 2 decrements the free variables , giving ? 3 ?% ( ? 1 ?% ). 24. Indeed, formulae in a tableau with unification may contain free variables , which are implicitly considered universally quantified. 25. We will assume the existence of such fixed points for every modal formula with one free variable . 26. Deriving a performance index requires that all free variables are removed, leaving only design variables and material variables. 27. Let's say we are given two first-order formulas \ alpha, \ beta-each of which has two free variables . 28. "' Reflection "': Let ? denote a first-order formula in which any number of free variables are present. 29. In the last case, there is no one-to-one correspondence between the free variables of the defining pair of identities. 30. The axioms should be read as universal closures; hence any free variables should be taken as tacitly universally quantified.
