[exec.domain.default]

namespace std::execution { struct default_domain { template<sender Sndr, queryable.. Env> requires (sizeof.(Env) <= 1) static constexpr sender decltype(auto) transform_sender(Sndr&& sndr, const Env&. env) noexcept(see below); template<sender Sndr, queryable Env> static constexpr queryable decltype(auto) transform_env(Sndr&& sndr, Env&& env) noexcept; template<class Tag, sender Sndr, class. Args> static constexpr decltype(auto) apply_sender(Tag, Sndr&& sndr, Args&&. args) noexcept(see below); }; }

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template<sender Sndr, queryable.. Env>
  requires (sizeof.(Env) <= 1)
constexpr sender decltype(auto) transform_sender(Sndr&& sndr, const Env&. env)
  noexcept(see below);

Let e be the expression tag_of_t<Sndr>().transform_sender(std::forward<Sndr>(sndr), env..) if that expression is well-formed; otherwise, std::forward<Sndr>(sndr).

Remarks: The exception specification is equivalent to noexcept(e).

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template<sender Sndr, queryable Env>
  constexpr queryable decltype(auto) transform_env(Sndr&& sndr, Env&& env) noexcept;

Let e be the expression tag_of_t<Sndr>().transform_env(std::forward<Sndr>(sndr), std::forward<Env>(env)) if that expression is well-formed; otherwise, FWD-ENV(std::forward<Env>(env)).

Returns: e.

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template<class Tag, sender Sndr, class. Args>
constexpr decltype(auto) apply_sender(Tag, Sndr&& sndr, Args&&. args)
  noexcept(see below);

Let e be the expression Tag().apply_sender(std::forward<Sndr>(sndr), std::forward<Args>(args).)

Remarks: The exception specification is equivalent to noexcept(e).