... term

A term is

1. a constant
2. a variable
3. a structure, consisting of a functor (which is a constant) followed by a sequence of terms enclosed in brackets and separated from one another by commas.

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...grandmother/2.

Note the standard conventional way of citing a Prolog predicate in the form predicate_name/arity.

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... programming.

For those of you who know about these things: Prolog does not contain 'while' loops, so recursion replaces loops.

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... argument:

The first/2 predicate could just as well have been defined as follows, with explicit calls to the unification operator =/2: first(List, First):- List = [HeadTail], First = Head. The version in the text has moved these calls from the body of the definition into the head of the definition (as a result of which the body is empty). This technique is called 'unfolding' and is a commonly used technique in Prolog programming.

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... 'no'.

This definition of member/2 can be simplified slightly by 'unfolding' the call to =/2 and placing it in the head of the rule, to give: member(Item, [ItemList]). member(Item, [_Tail]):- member(Item, Tail).

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... Expression

Remember that the equals sign is used in Prolog for unification, not arithmetic.

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... list:

length/2 comes predefined in SICStus Prolog. If you put this definition in a file and consult it, you will receive an error message. The solution is to rename the predicate in your definition, e.g. to mylength/2.

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