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plasp/encodings/strips/strips-incremental.lp

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% Constant '_parallel' to enable parallel actions
% - value '0': parallel actions *without* checking for mutual disablement
% - value '1': "forall" parallel actions that can be arranged in any sequence
% - value '2': "exists" parallel actions that can be arranged in some sequence
% - value '3': "exists" parallel actions omitting achievement of preconditions
% - value '4': "exists" parallel actions like '3' implemented by acyclicity
% - otherwise: sequential actions
#const _parallel = 5.
% Constant '_shallow' to cheaply approximate mutually disabling parallel actions
% - value '0': detect incompatible pre/postconditions to reduce parallel actions
% - otherwise: over-approximate parallel actions (in testing mutual disablement)
#const _shallow = 0.
% Constant 'planner_on' to enable encoding support for ASP-based planner
% - value '0': no compatibility to ASP-based planner (no idle steps permitted)
% - otherwise: compatibility to ASP-based planner (idle steps permitted)
#const planner_on = 0.
% BASE PROGRAM
% Define auxiliary predicates for actions w.r.t. parallel mode
selfdefeat(A,X) :- active(A), precondition(A,X,V), _parallel = 1,
has_condition(A,X,1), not postcondition(A,X,V).
diverge(A1,A2,X) :- active(A1), active(A2), postcondition(A1,X,V),
has_condition(A2,X,1), not postcondition(A2,X,V),
0 <= _parallel, _parallel < 5, _shallow = 0.
diverge(A1,A2) :- diverge(A1,A2,X).
exclude(A1,A2) :- active(A1), active(A2), precondition(A1,X,V),
has_condition(A2,X,0), not precondition(A2,X,V),
0 <= _parallel, _parallel < 5, _parallel != 2, _shallow = 0.
disable(A1,A2) :- active(A1), active(A2), A1 != A2, postcondition(A1,X,V),
has_condition(A2,X,0), not precondition(A2,X,V),
not diverge(A1,A2), not exclude(A1,A2),
1 < _parallel, _parallel < 5.
disable :- _parallel = 4, #sum{1,A1 : disable(A1,A2); -1,A2 : disable(A1,A2)} > 0.
scope(X,V) :- active(A), precondition(A,X,V), _parallel = 2.
% Define relevant fluents w.r.t. parallel mode
fluent(X,V) :- produce(X,V).
fluent(X,V) :- persist(X,V).
fluent(X,V) :- initialState(X,V), fluent(X).
fluent(X,V) :- active(A), postcondition(A,X,V), fluent(X).
fluent(X) :- fluent(X,V).
fluent(X) :- diverge(A1,A2,X), not exclude(A1,A2).
fluent(X) :- active(A), has_condition(A,X,1), 0 <= _parallel, _parallel < 5, _shallow != 0.
% Define unsubsumed mutexes
mutex(G,X) :- mutexGroup(G), contains(G,X,V), fluent(X,V).
mutex(G) :- mutexGroup(G), #count{X : mutex(G,X)} > 1.
% Define initial state
holds(X,V,0) :- initialState(X,V), fluent(X).
:- fluent(X), #count{V : holds(X,V,0)} > 1.
:- mutex(G), #count{X,V : holds(X,V,0), contains(G,X,V)} > 1.
% STEP PROGRAM
#program step(t).
% Generate successor state
1 {holds(X,V,t) : fluent(X,V)} 1 :- fluent(X).
:- mutex(G), #count{X,V : holds(X,V,t), contains(G,X,V)} > 1.
change(X,t) :- holds(X,V,t-1), not holds(X,V,t).
% Generate actions
{occurs(A,t)} :- active(A).
:- planner_on = 0, not occurs(A,t) : active(A).
:- occurs(A,t), postcondition(A,X,V), fluent(X), not holds(X,V,t).
effect(X,t) :- occurs(A,t), postcondition(A,X,V), fluent(X), not precondition(A,X,V).
:- change(X,t), not effect(X,t).
% Checks w.r.t. parallel mode
:- _parallel != 0, _parallel != 1, _parallel != 2, _parallel != 3, _parallel != 4,
#count{A : occurs(A,t)} > 1.
:- _parallel != 2, occurs(A,t), precondition(A,X,V), not holds(X,V,t-1).
:- _parallel = 1, occurs(A,t), precondition(A,X,V), not has_condition(A,X,1), not holds(X,V,t).
single(X,t) :- occurs(A,t), selfdefeat(A,X).
:- single(X,t), #count{A : occurs(A,t), postcondition(A,X,V), not precondition(A,X,V)} > 1.
proceed(X,V,t) :- holds(X,V,t-1), scope(X,V).
proceed(X,V,t) :- perform(A,t), scope(X,V), postcondition(A,X,V), not precondition(A,X,V),
occurs(A,t).
perform(A,t) :- active(A), 1 < _parallel, _parallel < 4,
proceed(X,V,t) : precondition(A,X,V), _parallel = 2;
alright(A1,t) : disable(A,A1).
alright(A,t) :- active(A), 1 < _parallel, _parallel < 4, not occurs(A,t).
alright(A,t) :- perform(A,t).
:- 1 < _parallel, _parallel < 4, active(A), not alright(A,t).
#edge((A1,t),(A2,t)) : disable(A1,A2), occurs(A1,t), _parallel = 4, not disable.
#edge((A1,t),(A2,t)) : disable(A1,A2), occurs(A2,t), disable.
% CHECK PROGRAM
#program check(t).
% Check goal conditions
:- query(t), goal(X,V), not holds(X,V,t).
% DISPLAY PART
#show occurs/2.