The notion of statement form (also called well-formed qormula) can be described more carefully than in the text. start with a collection of sym- bols that we agree to call statement letters. [do not allow the symbols , ~, v, λ, , ㈠ to be in this collection.] a statement letter is a statement form of the simplest kind; and if si and s2 are statement forms, then so are ~ (s), (s) v (s), (sj л (sj, (, and (s1) (s2). parentheses may be omitted when confusion is unlikely but they are sometimes essential: if si is p-o and s2 is q-r.