See ↑ MATERIAL 1, ↑ SUBJECT 1
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• ↑ be a matter of life and death/be a matter of life or death
• ↑ be no laughing matter
• ↑ be sth wrong with/be sth the matter with
• ↑ it doesn't matter
• ↑ no matter
• ↑ subject matter
• ↑ take it up with/take the matter up with
• ↑ what's wrong/what's the matter
• ↑ whoever/no matter who