There are two binary logical operations on constraints: conjunction
and disjunction.

A *conjunction* is a constraint taking two
operands.

If that is not satisfied, the conjunction is not satisfied.

Otherwise, the conjunction is satisfied if and only if the second
operand is satisfied.

A *disjunction* is a constraint taking two
operands.

If that is satisfied, the disjunction is satisfied.

Otherwise, the disjunction is satisfied if and only if the second
operand is satisfied.

[ Example

: *end example*

]template<typename T> constexpr bool get_value() { return T::value; } template<typename T> requires (sizeof(T) > 1) && get_value<T>() void f(T); // has associated constraint sizeof(T) > 1 ∧ get_value<T>() void f(int); f('a'); // OK: calls f(int)

In the satisfaction of the associated constraints
of f, the constraint sizeof(char) > 1 is not satisfied;
the second operand is not checked for satisfaction.

— [ Note

: *end note*

]A logical negation expression ([expr.unary.op]) is an atomic constraint;
the negation operator is not treated as a logical operation on constraints.

As a result, distinct negation constraint-expressions
that are equivalent under [temp.over.link]
do not subsume one another under [temp.constr.order].

Furthermore, if substitution to determine
whether an atomic constraint is satisfied ([temp.constr.atomic])
encounters a substitution failure, the constraint is not satisfied,
regardless of the presence of a negation operator.

[ Example

— : *end example*

]template <class T> concept sad = false; template <class T> int f1(T) requires (!sad<T>); template <class T> int f1(T) requires (!sad<T>) && true; int i1 = f1(42); // ambiguous, !sad<T> atomic constraint expressions ([temp.constr.atomic]) // are not formed from the same expression template <class T> concept not_sad = !sad<T>; template <class T> int f2(T) requires not_sad<T>; template <class T> int f2(T) requires not_sad<T> && true; int i2 = f2(42); // OK, !sad<T> atomic constraint expressions both come from not_sad template <class T> int f3(T) requires (!sad<typename T::type>); int i3 = f3(42); // error, associated constraints not satisfied due to substitution failure template <class T> concept sad_nested_type = sad<typename T::type>; template <class T> int f4(T) requires (!sad_nested_type<T>); int i4 = f4(42); // OK, substitution failure contained within sad_nested_type

Here,
requires (!sad<typename T::type>) requires
that there is a nested type that is not sad,
whereas
requires (!sad_nested_type<T>) requires
that there is no sad nested type.

—