Control

P,Q

prove P and Q

P;Q

prove P or Q

!

cut any choices taken in the current procedure

call(P)

prove (execute) P

\+ P

goal P is not provable

P->Q;R

if P succeeds, prove Q; if not, prove R

P->Q

if P succeeds, prove Q; if not, fail

true

succeed

otherwise

same as true

fail

fail (start backtracking)

false

same as fail

repeat

succeed repeatedly on backtracking