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Phrase(s): So be it.
This is the way it will be. • If you insist on running off and marrying her, so be it. Only don’t say I didn’t warn you! • Mary has decided that this is what she wants. So be it.
McGrawhill's American Idioms And Phrasal Verbs
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Let it be so, I accept it as it is. For example, If you can't change the reservation, so be it; I'll travel on Monday. This phrase, often given as a translation of the Hebrew (and Greek and Latin) amen, has been employed in the current sense since about 1600.
American Heritage Idioms