Non-terminal symbol `Formula`

Defining rules for nonterminal symbol Formula:

`Formula`		`Atomic`
		`AND` `OPENPAR` `Formulas_opt` `CLOSEPAR`
		`OR` `OPENPAR` `Formulas_opt` `CLOSEPAR`
		`EXISTS` `Vars` `OPENPAR` `Formula` `CLOSEPAR`
		`EXTERNAL` `OPENPAR` `Atom` `CLOSEPAR`

Occurrences of symbol Formula in body of other rules:

Non-terminal symbol Formula