Hi,
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Now, as for the mode needed with "Heureusement que", it's the indicative, because "heureusement" is considered as a sentence word [un mot-phrase]. The indicative is also wanted after: bien sûr que, bien entendu que, sans doute que, peut-être que, certainement que. In all these cases, "que" can be replaced by a comma.
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So I hope I would have given you a few more food for thought!
Note des modérateurs : Répondez seulement à la question grammaticale. Ne faites pas de relecture.