Predicates Like propositional variables, predicates start with an uppercase letter, followed by zero or more letters or digits. The arguments of the predicate are enclosed by brackets and separated by commas. Individual constants look exactly like propositional variables, i.e. they consist of one uppercase letter, followed by zero or more letters or digits. Individual constants denotate exactly one individual, each - hence the name. Invidual variables consist of one lowercase letter, followed by zero or more letters or digits.
Individual variables signify nothing.
The bound variable and the quantified expression, enclosed in brackets and separated by a comma, follow the quantifier. The syntax of proofs, too, resembles Lemmon's notation. The following example shows a proof which the gateway accepts without modifications. 2,6CP Explaining the deduction rules in detail would lead us a bit too far into detail. Often this is called 'modus ponens' or 'affirming the antecedent'.