Expressions
An expression is inductively defined as follows:
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a constant is an expression
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a variable is an expression
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a proper combination of expressions (by means of operators) is an expression.
They appear in specific parts of a Vadalog program, namely in operators, conditions and assignments, as we will see.
Other types of expressions in Vadalog are: negation, Skolem functions, equality-generating dependencies (EGDs), and negation as failure.