:: deftheorem defines PR-closure COMPUT_1:def 18 :
for Q being Subset of (HFuncs NAT) holds PR-closure Q = Q \/ { g where g is Element of HFuncs NAT : ex f1, f2 being Element of HFuncs NAT ex i being Element of NAT st
( f1 in Q & f2 in Q & g is_primitive-recursively_expressed_by f1,f2,i ) } ;