{P : Sort u} →
  {reason : Option Std.CancellationReason} →
    {consumers : Std.Queue Std.CancellationToken.Consumer} →
      {reason' : Option Std.CancellationReason} →
        {consumers' : Std.Queue Std.CancellationToken.Consumer} →
          { reason := reason, consumers := consumers } = { reason := reason', consumers := consumers' } →
            (reason = reason' → consumers = consumers' → P) → P