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11.2.4 Control

:P,:Q   ISO
prove P and Q
:P;:Q   ISO
prove P or Q
+M::P   ISO
call P in module M
:P->:Q;:R   ISO
if P succeeds, prove Q; if not, prove R
:P->:Q   ISO
if P succeeds, prove Q; if not, fail
!   ISO
cut any choices taken in the current procedure
\+ :P   ISO
goal P is not provable
?X ^ :P
there exists an X such that P is provable (used in setof/3 and bagof/3)
block :P   declaration
declaration that predicates specified by P should block until sufficiently instantiated
call(:P)   ISO
execute P or P(...)
Executes the procedure call Goal. When Goal succeeds determinately, is cut, fails, or raises an exception, Cleanup is executed.
Executes the procedure call Goal. Vars is unified with the list of new variables created during the call that remain unbound and have blocked goals or attributes attached to them.
+Iterators do :Body
executes Body iteratively according to Iterators
fail   ISO
fail (start backtracking)
same as fail
Blocks Goal until nonvar(Var) holds.
for each solution of P that succeeds, prove Q; if none, prove R
once(:P)   ISO
Find the first solution, if any, of goal P.
same as true
repeat   ISO
succeed repeatedly on backtracking
true   ISO
block Goal until Cond holds

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