A functional term consists of a function constant and an arbitrary number of argument terms, terminated by an optional sequence variable and surrounded by matching parentheses. A list term consists of the listof operator and a finite list of terms, terminated by an optional sequence variable and enclosed in matching parentheses. Quotations involve the quote operator and an arbitrary list expression . A list expression is either an atom or a sequence of list expressions surrounded by parentheses. An atom is either a word or a character reference or a character string or a character block.
Logical terms involve the if and cond operators.
The if form allows for the testing of a single condition or multiple conditions. An optional term at the end allows for the specification of a default value when all of the conditions are false. The cond form is similar but groups the pairs of sentences and terms within parentheses and has no optional term at the end. There are six types of sentences. We have already mentioned logical constants.