Conditional clauses can describe situations which have not yet happened, but are possible:
If it comes to court, you two can testify.
Here both verbs are in the present tense. Similar sentences can be constructed using unless:
Policemen don’t find bodies unless they are sent to look for them or unless someone else has found them first.
Here unless has the meaning of if . . . not … :
Policemen don’t find bodies if they aren’t sent to look for them or if someone else hasn’t found them first.
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