Free and bound 1. The well formed(wf) parts of b are the consecutive subformulas of B(including B itself) Which are wffs 2. An occurrence of a variable x in a wff b is bound iff it is in a wf part of b of the form VaC. otherwise it is free 3. The bound/ free varibles of a wff are those which have bound/ free occurrences in a wff (at different occurrences) 4. a wff without free individual variables is said to be a closed wff 5. A sentence is a wff without free variables of any type Logic in Computer Science -p 8/23Free and Bound 1. The well formed(wf) parts of B are the consecutive subformulas of B(including B itself) which are wffs. 2. An occurrence of a variable x in a wff B is bound iff it is in a wf part of B of the form ∀xC; otherwise, it is free. 3. The bound / free varibles of a wff are those which have bound / free occurrences in a wff (at different occurrences). 4. A wff without free individual variables is said to be a closed wff. 5. A sentence is a wff without free variables of any type. Logic in Computer Science – p.8/23