LISP has many different ideas of equality. Numerical equality is
denoted by =. Two symbols are eq if and only if they are
identical. Two
copies of the same list are not eq, but they are equal.
> (eq 'a 'a)
T
> (eq 'a 'b)
NIL
> (= 3 3)
T
> (= 3 4)
NIL
> (eq '(a b c) '(a b c))
NIL
> (equal '(a b c) '(a b c))
T
> (eql 'a 'a)
T
> (eql 3 3)
T
The eql predicate is equivalent to eq for symbols and to
= for numbers.
The equal predicate is equivalent to eql for symbols and
numbers. It is
true for two conses if and only if their cars are equal and their cdrs
are equal. It is true for two structures if and only if the structures
are the same type and their corresponding fields are equal.