## A selection property of the boolean $$\mu$$-calculus and some of its applications.(English)Zbl 0936.03030

Let $$\mathbb B$$ be the Boolean algebra of two elements 0 and 1, $$I$$ be a set of indices of arbitrary cardinality, $$\mathbb B^I$$ is a complete lattice with minimum 0 and maximum 1, $$f(x_1,\dots,x_n): (\mathbb B^I)^n\to\mathbb B^I$$ be a mapping monotonic in all its arguments, $$f_i(x_1,\dots,x_n): (\mathbb B^I)^n\to\mathbb B$$ be the component of $$f$$ of index $$i$$. It is assumed that for each index $$i\in I$$ there exists a set $$J_i$$ of indices of arbitrary cardinality such that $f_i(x_1,\dots,x_n) = \sum_{j\in J_i}f_{i,j}(x_1,\dots,x_n).$ A selector is a mapping $$\sigma$$ that associates with each $$i$$ in $$I$$ an element $$\sigma(i)$$ of $$J_i$$. Define $$f_\sigma(x_1,\dots,x_n): (\mathbb B^I)^n\to\mathbb B^I$$ as the mapping whose $$i$$-th component is $$f_{i,\sigma(i)}(x_1,\dots,x_n): (\mathbb B^I)^n\to\mathbb B$$. Let the quantities $$\mu$$ and $$\nu$$ be the least and the greatest correspondingly and every $$\theta_i$$ be $$\mu$$ or $$\nu$$.
Theorem. Let $$f$$ be defined as above and let $a = \theta_1 x_1\dots\theta_n x_n\cdot f(x_1,\dots,x_n)\in\mathbb B^I.$ Then there exists a selector $$\sigma$$ such that $a = \theta_1 x_1\dots\theta_n x_n\cdot f_{\sigma}(x_1,\dots,x_n).$ Applications to the McNaughton’s games on graphs and to modal $$\mu$$-calculus are given.
Reviewer: A.Nabebin (Moskva)

### MSC:

 03B70 Logic in computer science 68Q60 Specification and verification (program logics, model checking, etc.) 03D05 Automata and formal grammars in connection with logical questions 06B23 Complete lattices, completions 06E30 Boolean functions 68Q45 Formal languages and automata
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