std::experimental::ranges::EqualityComparable,(3)

NAME
std::experimental::ranges::EqualityComparable, - std::experimental::ranges::EqualityComparable,

Synopsis
   Defined in header <experimental/ranges/concepts>
   template< class T >
   concept bool EqualityComparable = WeaklyEqualityComparableWith<T, (1) (ranges TS)
   T>;
   template< class T, class U >
   concept bool EqualityComparableWith =
       EqualityComparable<T> &&
       EqualityComparable<U> &&
       CommonReference<
           const std::remove_reference_t<T>&, (2) (ranges TS)
           const std::remove_reference_t<U>&> &&
       EqualityComparable<
           ranges::common_reference_t<
               const std::remove_reference_t<T>&,
               const std::remove_reference_t<U>&>> &&
       WeaklyEqualityComparableWith<T, U>;
   1) The concept EqualityComparable<T> specifies that the comparison operators == and
   != on T reflects equality: == yields true if and only if the operands are equal.
   EqualityComparable<T> is satisfied only if, given objects a and b of type T, bool(a
   == b) is true if and only if a and b are equal. Together with the requirement that a
   == b is equality preserving, this implies that == is symmetric and transitive, and
   further that == is reflexive for all objects a that are equal to at least one other
   object.
   2) The concept EqualityComparableWith<T, U> specifies that the comparison operators
   == and != on (possibly mixed) T and U operands yield results consistent with
   equality. Comparing mixed operands yields results equivalent to comparing the
   operands converted to their common type.
   Formally, EqualityComparableWith<T, U> is satisfied only if, given any lvalue t of
   type const std::remove_reference_t<T> and any lvalue u of type const
   std::remove_reference_t<U>, and let C be ranges::common_reference_t<const
   std::remove_reference_t<T>&, const std::remove_reference_t<U>&>, bool(t == u) ==
   bool(C(t) == C(u)).
   Equality preservation
   An expression is equality preserving if it results in equal outputs given equal
   inputs.
     * The inputs to an expression consist of its operands.
     * The outputs of an expression consist of its result and all operands modified by
       the expression (if any).
   Every expression required to be equality preserving is further required to be
   stable: two evaluations of such an expression with the same input objects must have
   equal outputs absent any explicit intervening modification of those input objects.
   Implicit expression variations
   A requires-expression that uses an expression that is non-modifying for some
   constant lvalue operand also implicitly requires additional variations of that
   expression that accept a non-constant lvalue or (possibly constant) rvalue for the
   given operand unless such an expression variation is explicitly required with
   differing semantics. These implicit expression variations must meet the same
   semantic requirements of the declared expression. The extent to which an
   implementation validates the syntax of the variations is unspecified.