A formation rule specifies how well-formed expressions can be constructed from simpler expressions in a formal language. The formal grammar of propositional formulas has rules for propositional variables, negation and binary logical implication.
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The term "formation rule" can refer to different concepts depending on the context in which it is used. Here are a few interpretations: 1. **Mathematics and Logic**: In formal systems, a formation rule specifies how certain symbols can be combined to form valid expressions or statements. For example, in formal grammars, a formation rule might determine how to construct sentences from a set of symbols.