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### 2.7 Equality Predicates

Here we describe functions that test for equality between two objects. Other functions test equality of contents between objects of specific types, e.g., strings. For these predicates, see the appropriate chapter describing the data type.

— Function: eq object1 object2

This function returns `t` if object1 and object2 are the same object, and `nil` otherwise.

If object1 and object2 are integers with the same value, they are considered to be the same object (i.e., `eq` returns `t`). If object1 and object2 are symbols with the same name, they are normally the same object—but see Creating Symbols for exceptions. For other types (e.g., lists, vectors, strings), two arguments with the same contents or elements are not necessarily `eq` to each other: they are `eq` only if they are the same object, meaning that a change in the contents of one will be reflected by the same change in the contents of the other.

```          (eq 'foo 'foo)
⇒ t

(eq 456 456)
⇒ t

(eq "asdf" "asdf")
⇒ nil

(eq "" "")
⇒ t
;; This exception occurs because Emacs Lisp
;; makes just one multibyte empty string, to save space.

(eq '(1 (2 (3))) '(1 (2 (3))))
⇒ nil

(setq foo '(1 (2 (3))))
⇒ (1 (2 (3)))
(eq foo foo)
⇒ t
(eq foo '(1 (2 (3))))
⇒ nil

(eq [(1 2) 3] [(1 2) 3])
⇒ nil

(eq (point-marker) (point-marker))
⇒ nil
```

The `make-symbol` function returns an uninterned symbol, distinct from the symbol that is used if you write the name in a Lisp expression. Distinct symbols with the same name are not `eq`. See Creating Symbols.

```          (eq (make-symbol "foo") 'foo)
⇒ nil
```

The Emacs Lisp byte compiler may collapse identical literal objects, such as literal strings, into references to the same object, with the effect that the byte-compiled code will compare such objects as `eq`, while the interpreted version of the same code will not. Therefore, your code should never rely on objects with the same literal contents being either `eq` or not `eq`, it should instead use functions that compare object contents such as `equal`, described below. Similarly, your code should not modify literal objects (e.g., put text properties on literal strings), since doing that might affect other literal objects of the same contents, if the byte compiler collapses them.

— Function: equal object1 object2

This function returns `t` if object1 and object2 have equal components, and `nil` otherwise. Whereas `eq` tests if its arguments are the same object, `equal` looks inside nonidentical arguments to see if their elements or contents are the same. So, if two objects are `eq`, they are `equal`, but the converse is not always true.

```          (equal 'foo 'foo)
⇒ t

(equal 456 456)
⇒ t

(equal "asdf" "asdf")
⇒ t
(eq "asdf" "asdf")
⇒ nil

(equal '(1 (2 (3))) '(1 (2 (3))))
⇒ t
(eq '(1 (2 (3))) '(1 (2 (3))))
⇒ nil

(equal [(1 2) 3] [(1 2) 3])
⇒ t
(eq [(1 2) 3] [(1 2) 3])
⇒ nil

(equal (point-marker) (point-marker))
⇒ t

(eq (point-marker) (point-marker))
⇒ nil
```

Comparison of strings is case-sensitive, but does not take account of text properties—it compares only the characters in the strings. See Text Properties. Use `equal-including-properties` to also compare text properties. For technical reasons, a unibyte string and a multibyte string are `equal` if and only if they contain the same sequence of character codes and all these codes are in the range 0 through 127 (ASCII).

```          (equal "asdf" "ASDF")
⇒ nil
```

However, two distinct buffers are never considered `equal`, even if their textual contents are the same.

The test for equality is implemented recursively; for example, given two cons cells x and y, `(equal `x y`)` returns `t` if and only if both the expressions below return `t`:

```     (equal (car x) (car y))
(equal (cdr x) (cdr y))
```

Because of this recursive method, circular lists may therefore cause infinite recursion (leading to an error).

— Function: equal-including-properties object1 object2

This function behaves like `equal` in all cases but also requires that for two strings to be equal, they have the same text properties.

```          (equal "asdf" (propertize "asdf" 'asdf t))
⇒ t
(equal-including-properties "asdf"
(propertize "asdf" 'asdf t))
⇒ nil
```