# xor, _xor

Logical exclusive-or

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b1 xor b2
_xor(b1, b2, …)

## Description

b1 xor b2 represents the exclusive logical or of the Boolean expressions b1, b2.

xor is defined as follows: a xor b is equivalent to (a or b) and not (a and b).

MuPAD® uses a three state logic with the Boolean constants TRUE, FALSE, and UNKNOWN. These are processed as follows:

 or TRUE FALSE UNKNOWN TRUE TRUE TRUE TRUE FALSE TRUE FALSE UNKNOWN UNKNOWN TRUE UNKNOWN UNKNOWN

Boolean expressions can be composed of these constants as well as of arbitrary arithmetical expressions. Typically, equations, such as x = y, and inequalities, such as x <> y, x < y, x <= y, are used to construct Boolean expressions.

_xor(b1, b2, ...) is equivalent to b1 xor b2 xor .... This expression represents TRUE if an odd number of operands evaluate to TRUE and the others evaluate to FALSE. It represents FALSE if an even number of operands evaluate to TRUE and the others evaluate to FALSE. It represents UNKNOWN if at least one operand evaluates to UNKNOWN.

Combinations of the constants TRUE, FALSE, UNKNOWN inside a Boolean expression are simplified automatically. However, symbolic Boolean subexpressions, equalities, and inequalities are not evaluated and simplified by logical operators. Use bool to evaluate such expressions to one of the Boolean constants. Note, however, that bool can evaluate inequalities x < y, x <= y, and so on only if they are composed of numbers of type Type::Real. See Example 2.

Use simplify with the option logic to simplify expressions involving symbolic Boolean subexpressions. See Example 3.

The precedences of the logical operators are as follows. If in doubt, use parentheses to ensure that the expression is parsed as desired.

• The operator not is stronger binding than and, that is, not b1 and b2 = (not b1) and b2.

• The operator and is stronger binding than xor, that is, b1 and b2 or b3 = (b1 and b2) xor b3.

• The operator xor is stronger binding than or, that is, b1 xor b2 or b3 = (b1 xor b2) or b3.

• The operator or is stronger binding than ==>, that is, b1 or b2 ==> b3 = (b1 or b2) ==> b3.

• The operator ==> is stronger binding than <=>, that is, b1 ==> b2 <=> b3 = (b1 ==> b2) <=> b3.

In the conditional context of if, repeat, and while statements, Boolean expressions are evaluated via “lazy evaluation” (see _lazy_and, _lazy_or). In any other context, all operands are evaluated.

## Examples

### Example 1

Combinations of the Boolean constants TRUE, FALSE, and UNKNOWN are simplified automatically to one of these constants:

TRUE and (FALSE xor TRUE)

FALSE xor UNKNOWN, TRUE xor FALSE

### Example 2

Logical operators simplify subexpressions that evaluate to the constants TRUE, FALSE, UNKNOWN.

b1 xor b2 and TRUE

FALSE xor ((not b1) and TRUE)

b1 and (b2 xor FALSE) and UNKNOWN

FALSE or (b1 and UNKNOWN) xor x < 1

TRUE xor ((b1 and FALSE) or (b1 and TRUE))

However, equalities and inequalities are not evaluated:

(x = x) and (1 < 2) and (2 < 3) xor (3 < 4)

Boolean evaluation is enforced via bool:

bool(%)

### Example 3

Expressions involving symbolic Boolean subexpressions are not simplified by and, or, not. Simplification has to be requested explicitly via the function simplify:

(b1 and b2) xor (b1 and (not b2)) and (1 < 2)

simplify(%, logic)

## Parameters

 b1, b2, … Boolean expressions

## Return Values

Boolean expression.

b, b_1, b_2

## See Also

### MuPAD Functions

#### Mathematical Modeling with Symbolic Math Toolbox

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