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Terms are evaluated next and consist of a sequence of factors, separated by multiplying operators (* , I, di v, mod, and) or alternatively, simply a factor by itself. 

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Simple expressions are evaluated after terms and consist of a sequence of terms, separated by adding operators (+, -,or) or alternatively, simply a term by itself. An optional sign-inversion operator (+, -) may prefix the first term of a simple expression. 

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Finally expressions are evaluated. These comprise a simple expression, a relational operator (=, <>, <=, >=, >, in) and another simple expression, or simply a simple expression itself. 

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