std::unary_negate - Man Page

typedef _Predicate::argument_type argument_type
argument_type is the type of the argument
typedef bool result_type
result_type is the return type

constexpr unary_negate (const _Predicate &__x)
constexpr bool operator() (const typename _Predicate::argument_type &__x) const

_Predicate _M_pred

class std::unary_negate< _Predicate >"One of the negation functors.

argument_type is the type of the argument

result_type is the return type