1 Ackermann = WF_Rel +
2 consts ack :: "nat * nat => nat"
3 recdef ack "measure(%m. m) ** measure(%n. n)"
4 "ack(0,n) = Suc n"
5 "ack(Suc m,0) = ack(m, 1)"
6 "ack(Suc m,Suc n) = ack(m,ack(Suc m,n))"
7 end