Some definitions of interest.
prime_nats	Def  Prime == {x:| prime(x) }
nat	Def   == {i:| 0i }
	Thm*    Type
prime_mset_complete	Def  prime_mset_complete(f)(x) == if is_prime(x) f(x) else 0 fi
	Thm*  f:(Prime). prime_mset_complete(f)
prime_decider	Def  is_prime(x) == prime_decider_exists{1:l}(x)
	Thm*  x:. is_prime(x)

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