# Tree automata and logic programs

## Abstract

Each clause of a definite sentence can be read as a move of a tree automaton. These tree automata, called pattern replacing automata (PRA), are introduced and studied in this paper.

- (a)
Each PRA (and hence each definite sentence) can be put into particularly simple forms ; for definite sentences these special forms are as follows : (1) in each clause the premise contains all the variables of the conclusion ; (2) in each clause all variables of the premise appear also in the conclusion ; and (3) in each clause the height of the terms of the premise is one at most and the height of the terms of the conclusion is two at most.

- (b)
The class of tree languages recognized by a restricted class of PRA, called monadic weak PRA, coincides with the class of recognizable tree languages.

The rest of the paper consists of two sections. In section 1 we shortly give the necessary definitions and in section 2 we intuitively explain the results mentioned above.

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## References

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