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The School of Divination wizard's Portent feature says, in part (Player's Handbook, page 116):

You can replace any attack roll, saving throw, or ability check made by you or a creature that you can see with one of these foretelling rolls. You must choose to do so before the roll, and you can replace a roll in this way only once per turn.

The "Advantage and Disadvantage" section states (Player's Handbook, page 173):

When you have advantage or disadvantage and something in the game, such as the halfling’s Lucky trait, lets you reroll the d20, you can reroll only one of the dice.

How do these rules interact?

  • Does the Portent feature fall under this section of the "Advantage and Disadvantage" rules?
  • When using the Portent feature with advantage or disadvantage, do you replace the entire "attack roll, saving throw, or ability check", or just one of the dice?
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11 Answers 11

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The halfling's Lucky trait deals with the die roll (PHB, p. 28):

When you roll a 1 on an attack roll, ability check, or saving throw, you can reroll the die and must use the new roll.

And so does Advantage/Disadvantage, since it refers to the same trait (PHB, p. 173):

For example, if a halfling has advantage on an ability check and rolls a 1 and a 13, the halfling could use the Lucky trait to reroll the 1.

The Divination wizard's Portent feature, on the other hand, deals with the check as a whole:

You can replace any attack roll, saving throw, or ability check ... with one of these foretelling rolls.

And here comes the interesting part - the three emphasized terms are only mentioned in rules as actions, not numbers:

  • The description of attack rolls (PHB, p. 194):

    To make an attack roll, roll a d20 and add the appropriate modifiers. If the total of the roll plus modifiers equals or exceeds the target’s Armor Class (AC), the attack hits.

  • Saving throws (PHB, p. 179):

    To make a saving throw, roll a d20 and add the appropriate ability modifier. [...]

    A saving throw can be modified by a situational bonus or penalty [...]

    [...] proficiency in a saving throw lets a character add his or her proficiency bonus to saving throws made using a particular ability score. [...]

  • And ability checks (PHB, p. 171):

    To make an ability check, roll a d20 and add the relevant ability modifier. As with other d20 rolls, apply bonuses and penalties, and compare the total to the DC.

All three go the standard way:

  1. Roll a d20, get a number
  2. In case of (dis-)advantage: roll another d20, get a new number (or keep the old)
  3. Add bonuses/penalties, get the final number
  4. Compare the final number with the AC/DC and get the final success/failure answer

From the strict RAW reading of Portent, we have to replace steps 1–4 (the whole check) with a number (foretelling roll), which makes no sense, as the result has to be boolean – success/failure.

If we loosen the restrictions, the logical thing to say would be "In the context of Portent, attack roll/saving throw/ability check is the number to be compared with the AC/DC" (i.e. the result of Step 3 above). In this interpretation "You must choose to do so before the roll" means that the decision is made before Step 1 and therefore no actual die roll happens. The modifiers are applied to the foretold roll as normal. This interpretation is reinforced by an unofficial tweet from March 2015 by rules designer Jeremy Crawford:

The portent die is intended to replace a d20 roll only, not any modifiers applied to it.

This result is Rules As Intended as well; the whole point is that the character knows in advance what is going to happen.

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    \$\begingroup\$ Your answer seems to leave out the relevant part of the advantage/disadvantage rule, specifically the 2 preceding sentences. The 2018 PHB errata changed both mentions of "reroll" there to "reroll or replace": "When you have advantage or disadvantage and something in the game, such as the halfling's Lucky trait, lets you reroll or replace the d20, you can reroll or replace only one of the dice." Since Portent says it replaces the roll, it clearly now falls under that rule. You may want to update your answer accordingly. \$\endgroup\$ – V2Blast Oct 3 at 21:35
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    \$\begingroup\$ @V2Blast I actually disagree. If this interpretation is correct (and the community generally believes it is), then Portent is still not replacing a d20 but the entire check. No dice are rolled, you replace the check itself with a result. This also fits the context of the ability, where the Diviner "knows" the end result. Applying (dis)advantage using the foretelling as a single die does not accomplish this flavor. \$\endgroup\$ – Ifusaso Oct 9 at 18:01
  • \$\begingroup\$ Your interpretation of the rules leads to this logic "portent replaces the result of Step 3 above" (shortened). Because that is what is meant by an attack roll etc. However then you state that modifiers are applied as normally without any reasoning, just so you are in line of the (not official) ruling of crawford. Could you add some reasoning to that step or consider removing it as it is part of this separate question. Otherwise this answer gives an unexplained answer rpg.stackexchange.com/questions/176302/… \$\endgroup\$ – findusl Oct 10 at 19:35
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You've quoted the applicable rules, but I'm going to repeat the quote of the Portent feature here with bold added for emphasis:

You can replace any attack roll, saving throw, or ability check made by you or a creature that you can see with one of these foretelling rolls. You must choose to do so before the roll, and you can replace a roll in this way only once per turn.

An attack roll with advantage or disadvantage is still an attack roll, not two attack rolls. Likewise for saving throws and ability checks. You're not replacing the roll of a die, you're replacing the result of an attack roll, saving throw, or ability check.

As for the second rule you quote on advantage/disadvantage, I've repeated it here with bold added for emphasis:

When you have advantage or disadvantage and something in the game, such as the halfling’s Lucky trait, lets you reroll the d20, you can reroll only one of the dice.

The Portent feature clearly doesn't come under this rule, since its effect is not a reroll of any kind.

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    \$\begingroup\$ The 2018 PHB errata changes both mentions of "reroll" in the Advantage rule to "reroll or replace". Since Portent says it replaces the roll, it clearly now falls under the rule. You may want to update your answer accordingly. \$\endgroup\$ – V2Blast Jun 27 '19 at 10:35
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New Answer - 2018 Errata

The 2018 PHB Errata changes the wording of Advantage and Disadvantage to

When you have advantage or disadvantage and something in the game, such as the halfling’s Lucky trait, lets you reroll or replace the d20, you can reroll or replace only one of the dice. You choose which one. For example, if a halfling has advantage on an ability check and rolls a 1 and a 13, the halfling could use the Lucky trait to reroll the 1.

Therefore, the new answer is that the portent dice only can replace one of the dice that were rolled. For example, consider the sequence of events

  1. The wizard declares he is using Portent before the roll. For example, he declares an attack and uses his 18 roll.
  2. The wizard rolls 2 die due to advantage or disadvantage. E.g. rolls 2 and 10 with disadvantage.
  3. The 2 is replaced by the 18.
  4. Disadvantage resolves. The resulting dice is 10.

Old Answer

This section is maintained for historical purpose. This answer is no longer correct due to the 2018 Errata.

black_fm answered the question, but since then, we've actually gotten an official response from Crawford on Twitter. Also note: Crawford's tweets are no longer official rulings.

The way it works, as written by Crawford (or at least how I understand his tweet), is:

  1. The wizard declares he is using Portent before the roll. For example, he declares an attack and uses his 18 roll.
  2. The wizard rolls 2 die due to advantage or disadvantage. E.g. rolls 2 and 19 with disadvantage.
  3. The advantage/disadvantage resolves. The result is a roll of 2.
  4. The 2 is replaced by the 18.

Note that steps 2 and 3 are "useless" since they are being replaced by the 18 anyway. But it might help to understand what an "attack roll" means in the Portent writing sense - it's the resulting roll (in the example, 2) from the action.

As mentioned by black_fm, this makes sense when you read the Portent as "the Wizard knows exactly what is going to happen" - it means he knows he is going to hit his spell even when the enemy is hidden (i.e. even with disadvantage).

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  • \$\begingroup\$ Comments are not for extended discussion; this conversation has been moved to chat. \$\endgroup\$ – V2Blast Oct 9 at 7:52
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I think the best thing to do here is to compare the wording on Lucky and Portent:

Halflings, PHB 28 (emphasis mine):

Lucky. When you roll a 1 on an attack roll, ability check, or saving throw, you can reroll the die and must use the new roll.

Portent, PHB 116 (emphasis mine):

You can replace any attack roll, saving throw, or ability check made by you or a creature that you can see with one of these foretelling rolls. You must choose to do so before the roll, and you can replace a roll in this way only once per turn.

As you can see, both use the same wording (aside from a difference in ordering), so it should be assumed that they work in the same way and that each replaces the same things.

Advantage and Disadvantage, PHB 173 (emphasis mine):

When you have advantage or disadvantage and something in the game, such as the halfling’s Lucky trait, lets you reroll the d20, you can reroll only one of the dice. You choose which one.

The way this is worded, it is meant as a general rule, with Lucky as an example, rather than the only case. Since Lucky and Portent both replace the same thing, we can then surmise that this means that Portent interacts with Advantage and Disadvantage in the same way.

Thus, using Portent allows you to replace one of the rolls you make when you have advantage or disadvantage, before you roll them.

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    \$\begingroup\$ This answer seems to match Crawford's recent tweet in that a die roll is replaced, but any bonuses still apply to the replacement roll. Is that how you read it? \$\endgroup\$ – KorvinStarmast Aug 18 '16 at 18:46
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    \$\begingroup\$ Not quite. Portent replaces what would be the resultant roll of Advantage or Disadvantage. See here. sageadvice.eu/2016/03/24/diviner-wizard-portent \$\endgroup\$ – jprepo1 Feb 12 '18 at 11:28
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    \$\begingroup\$ Portent doesn't let you reroll, it replaces the roll, before it is rolled. So it doesn't fit that clause of Adv/Dis. \$\endgroup\$ – Adeptus May 17 '18 at 3:27
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    \$\begingroup\$ The 2018 PHB errata changes both mentions of "reroll" in the Advantage rule to "reroll or replace". Since Portent says it replaces the roll, it clearly now falls under the rule. You may want to update your answer accordingly. \$\endgroup\$ – V2Blast Jun 27 '19 at 10:36
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There are two logical conclusions here, and neither one of them is particularly satisfying.

  • The first and most obvious is that advantage/disadvantage is ignored, and you replace the entire roll with the chosen die.

  • The second is that you extend the ruling on pg 173 to include straight up die replacement in addition to rerolls and then roll a second die to see if you do better/worse than you replacement die.

Neither of these rulings is particularly satisfactory to me. The first removes disadvantage/advantage from play entirely. This can be good (replacing disadvantage) or largely unnecessary (replacing advantage). The second means that it's almost never a good idea to use this power at all when you have advantage/disadvantage, and relies on an extension of a rule that I find a tenuous though plausible leap.

The second interpretation basically relies on redefining this as a pre-reroll, which you could definitely make the case that it is. But at the same time, I find the idea a bit of a stretch.

Both of these are pretty unsatisfactory though. However, all is not lost. Most rolls in the game are not subject to advantage/disadvantage, and thus, this ability is super useful without needing to delve into this complication.

So pick an interpretation that works for your table, and go with that. However, more importantly, don't get too hung up on this because it's not super likely to come up, and even if it is, it's one roll.

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  • \$\begingroup\$ The 2018 PHB errata changes both mentions of "reroll" in the Advantage rule to "reroll or replace". Since Portent says it replaces the roll, it clearly now falls under the rule. You may want to update your answer accordingly. \$\endgroup\$ – V2Blast Jun 27 '19 at 10:37
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On Twitter, Jeremy Crawford replies to a tweet:

"The portent die is intended to replace a d20 roll only, not any modifiers applied to it."

As much as I agree with black_fm's textual analysis...

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    \$\begingroup\$ This is almost just a comment, not an answer, but if you expand it to contain your full position (so your answer will remain valid even if the others are deleted), it'd be great. \$\endgroup\$ – user17995 Aug 11 '15 at 2:11
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When you use Portent to replace a roll with advantage or disadvantage, you replace one of the two d20s.

This has been clearly addressed by the 2018 PHB errata:

Advantage and Disadvantage (p. 173). In the first sentence of the fourth paragraph, both instances of “reroll” have been changed to “reroll or replace.”

The relevant portion of the rule on Advantage and Disadvantage in the PHB and Basic Rules now reads (emphasis mine):

When you have advantage or disadvantage and something in the game, such as the halfling's Lucky trait, lets you reroll or replace the d20, you can reroll or replace only one of the dice. You choose which one. For example, if a halfling has advantage or disadvantage on an ability check and rolls a 1 and a 13, the halfling could use the Lucky trait to reroll the 1.

Previously, that portion of the rule only applied to features that let you reroll a d20 after the initial roll, but now that has been expanded to features that let you replace the die instead of rerolling it - like the School of Divination wizard's Portent feature (PHB, p. 116):

You can replace any attack roll, saving throw, or ability check made by you or a creature that you can see with one of these foretelling rolls. You must choose to do so before the roll, and you can replace a roll in this way only once per turn.

As of the 2018 PHB errata, it is clear that when you use Portent to replace an attack roll, ability check, or saving throw that you have advantage or disadvantage on, you replace one of the two die rolls (before you make it), and then roll the other die. You then apply the advantage/disadvantage rules as normal.


For reference, the Portent feature replaces only the d20, not the entire roll; modifiers are still added to it. This is supported by this unofficial tweet from March 2015 by rules designer Jeremy Crawford:

When using a Diviner's portent die, are modifiers added to the portent die, or is the portent die used as is?

The portent die is intended to replace a d20 roll only, not any modifiers applied to it.

As well as this unofficial tweet from April 2016:

Sorry, follow up: and does diviner's portent replace roll only or roll plus modifiers? Thanks again.

A Portent roll replaces a d20 roll, not modifiers.

As such, it is clear that, post-errata, Portent replaces only one of the dice when rolling at advantage or disadvantage. After advantage or disadvantage is applied, modifiers are added to the die as usual to determine the total for the roll.

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Portent does not interact with advantage/disadvantage because it replaces an entire roll.

The 2020 Sage Advice Compendium makes clear on p. 1 that Jeremy Crawford's tweets are no longer official rulings but may preview future rulings. In other words, these tweets are no longer official but instead provide insight into RAI. The Sage Advice Compendium currently offers no official guidance on this question.

Portent allows you to "replace any attack roll, saving throw, or ability check made by you or a creature that you can see with one of these foretelling rolls. You must choose to do so before the roll..." (Compare with Lucky, which allows you to "reroll a die" when "you roll a 1 on the d20.")

The PHB under "Ability Checks" (p. 174) seems to define an ability check as
d20 roll + ability modifier + bonuses - penalties.
Under "Saving Throws" (p. 179), it seems to define a saving throw as d20 roll + ability modifier + situational bonus - situational penalty.
Under "Attack Rolls" (p. 194) it seems to define an attack roll as d20 roll + appropriate modifiers.

If this is true—and I can't wait to log in tomorrow morning and find out it's not—then Portent replaces the entire roll, i.e. d20 + mods, with the Portent die roll. Advantage and disadvantage don't enter into the equation because they only affect the d20 result, which is but a component of the replaced attack roll, saving throw, or ability check.

This is my understanding of RAW, and it obviously goes against RAI, as evidenced by Crawford's tweets. There's a case to be made, and others have made it here, that Portent should replace only one d20 on an advantage or disadvantage roll. Personally, I prefer (and use) the idea that the d20 replaces the final d20 result of advantage or disadvantage, because it is the ruling that always makes a PC's use of Portent impactful.

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    \$\begingroup\$ the d20 replaces the final d20 result of advantage or disadvantage, because it is the ruling that always makes a PC's use of Portent impactful.: I completely agree. By RAW, you should replace one of the 2 rolls, this weakens the Portent ability. \$\endgroup\$ – Eddymage Oct 3 at 14:31
  • \$\begingroup\$ @Eddymage: I assume "I completely agree" is meant to agree with the latter part of that sentence (that Portent replacing the final result of the roll with advantage/disadvantage makes it a better feature), since you disagree with the answer's claim (that Portent replacing the final result of the roll with advantage/disadvantage is RAW in the first place). \$\endgroup\$ – V2Blast Oct 3 at 21:09
  • \$\begingroup\$ @V2Blast Yes, I agree with the enlighten part, not with the answer as I explained in my own. \$\endgroup\$ – Eddymage Oct 3 at 21:31
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    \$\begingroup\$ @Eddymage: I figured, just wanted to clarify since you did say "I completely agree" even though you only agreed with part of what you quoted :P \$\endgroup\$ – V2Blast Oct 3 at 21:32
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It depends on who's affecting whom

First the basics. After the 2018 PHB Errata, the relevant paragraph from the Advantage and Disadvantage section now reads:

When you have advantage or disadvantage and something in the game, such as the halfling's Lucky trait, lets you reroll or replace the d20, you can reroll or replace only one of the dice.

Portent replaces the d20, not the d20+modifiers, so this rule definitely applies. However, the use of 'you' throughout that sentence adds an interesting wrinkle.

Situation 1: the wizard uses it on their own roll

A Divination wizard has disadvantage on attack rolls, due to the frightened condition. The wizard...

  1. Takes the Attack action.
  2. Declares that they are using their Portent roll (a 17) on the attack roll.
  3. Rolls a single d20, which takes the place of the second roll (required by disadvantage).
  4. Must use the lower of the 17 (the Portent roll) and the d20 they rolled.

Situation 2: the wizard uses it on someone else's roll

A Divination wizard is facing off against a glabrezu. The glabrezu has advantage on saving throws against spells and other magical effects, due to the Magic Resistance trait. The wizard...

  1. Casts shatter and includes the glabrezu in the area.
  2. Declares that they are using their Portent roll (a 3) on the glabrezu's Constitution saving throw.
  3. Laughs as the glabrezu must use the 3 plus its Constitution saving throw modifier.

This situation is different, because the advantage/disadvantage wording only applies if you have advantage or disadvantage and something lets you replace the d20. The creature under the affect of the advantage or disadvantage must be the same creature doing the replacement for the d20 replacement restriction to apply.

To be clear, the same applies if an NPC wizard uses Portent to replace a PC's roll. 'You' in the PHB refers to any creature - it isn't limited to PCs, unless otherwise noted. What matters in this case is - are the Portent user and the creature with advantage/disadvantage the same creature?

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  • \$\begingroup\$ While I agree with the 1st situation, in the 2nd one I am not completely convinced that the you pronoun in Advantage/disadvantage wording has to be intended as you player and not as you creature: in this way this ruling really advantages (ah ah) players, leading to unbalanced mechanics that heavily disfavors enemies and NPC. \$\endgroup\$ – Eddymage Oct 4 at 9:24
  • \$\begingroup\$ @Eddymage The use of 'you' doesn't just refer to the player. That said, the three uses of 'you' throughout the sentence refer to the same creature. That creature may be an NPC or a PC, but either way, the rule only applies if a creature is affecting their own d20. I've edited in a clarifying paragraph. \$\endgroup\$ – Red Orca Oct 4 at 14:52
  • \$\begingroup\$ Thanks, it is clearer now. But I strongly disagree. Let translate your 2nd situation into the words of adv/disadv: When you (Glabrezu) have advantage or disadvantage and something in the game (wizard's Portent) [...] lets you (Glabrezu) reroll or replace the d20, you (Glabrezu) can reroll or replace only one of the dice. Then, Portent does not work as you described, but it allows to replace one of the two dice from the advantage/disadvantage. \$\endgroup\$ – Eddymage Oct 4 at 18:14
  • \$\begingroup\$ @Eddymage The glabrezu isn't the one replacing the d20 - the Divination wizard is. The glabrezu having their d20 replaced is not the same as the glabrezu replacing their d20. \$\endgroup\$ – Red Orca Oct 5 at 16:37
  • \$\begingroup\$ I see this active/passive distinction completely wrong, as I depicted in my comment above: the "something in the game" makes the Glabrezu replace the roll, hence it falls under the same circumstances (i.e., ruling) of the 1st. \$\endgroup\$ – Eddymage Oct 5 at 19:52
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By RAW, you can choose only 1 of the 2 dice rolled with Adv/Disadv to be replaced by the Portent score.

Under the 2018 PHB errata, the paragraph at pag 173 of PHB now reads (emphasis mine)

When you have advantage or disadvantage and something in the game, such as the halfling's Lucky trait, lets you reroll or replace the d20, you can reroll or replace only one of the dice. You choose which one. For example, if a halfling has advantage on an ability check and rolls a 1 and a 13. the halfling could use the Lucky trait to reroll the I.

The Portent feature still reads (emphasis mine)

You can replace any attack roll, saving throw, or ability check made by you or a creature that you can see with one of these foretelling rolls. You must choose to do so before the roll, and you can replace a roll in this way only once per turn.

Hence you can choose only one die to be replaced with the score given by Portent feature. Since you must choose to do so before the roll (hence before knowing the two rolls) you choose which one: if you have only one die, then decide beforehand to replace the 1st or the 2nd die; if you have several d20 dice, maybe colored, then you decide to roll at the same time the red and the yellow and say that you will replace the red one.


Another answer pointed out that the Portent ability replace any attack roll, saving throw, or ability check [...], then the final result is replaced by the Portent die, without considering also any modifiers. But the PHB (pag 7, "The D20", 3rd paragraph) says (emphasis mine)

Ability checks, attack rolls, and saving throws are the three main kinds of d20 rolls, forming the core of the rules of the game.

Under the ability check section (pag 174), it says

To make an ability check, roll a d20 and add the relevant ability modifier.

Similar wording for saving throws and attack rolls. Hence, Portent ability must be read as it allows to replace just a roll of the d20 die, not the final result, since its description reads as you can replace a roll in this way only once per turn and not the final outcome.

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    \$\begingroup\$ I'm not exactly sure why this is getting so many downvotes... Perhaps the hard-to-understand statistical breakdown in the middle? But the logic of the first and last sections seems to be correct. \$\endgroup\$ – V2Blast Oct 9 at 7:49
  • \$\begingroup\$ @V2Blast Honestly, I do not know, anyone is not giving explanation for downvotes... maybe you're right, the probabilistic part is hard to get or poorly written. \$\endgroup\$ – Eddymage Oct 9 at 7:53
  • \$\begingroup\$ I removed the probabilistic part, since it seems to generate confusion rather than clarifying. \$\endgroup\$ – Eddymage Oct 9 at 17:49
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Thematically Speaking, I would say that it completely ignores advantage/disadvantage rules. Remember that the ability is based on seeing the future and knowing specifically what will happen. This is not a case of luck (rolling of the dice), it is essentially setting the event to occurring as predicted. Therefore it would ignore any circumstances as such.

In addition, being told that portent doesn't replace both dice in such a situation makes numerous players far more reluctant to ever play the divination school in comparison to the many others.

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