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forbidden interval update
Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>
This commit is contained in:
Nikolaj Bjorner
parent
e6c4ae19c6
commit
a6643955e6
7 changed files with 192 additions and 242 deletions
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@ -89,7 +89,7 @@ namespace polysat {
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LOG_H3("Computing forbidden interval for: " << c);
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eval_interval interval = eval_interval::full();
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signed_constraint neg_cond;
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if (c->forbidden_interval(s, c.is_positive(), v, interval, neg_cond)) {
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if (get_interval(s, c, v, interval, neg_cond)) {
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LOG("interval: " << interval);
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LOG("neg_cond: " << neg_cond);
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if (interval.is_currently_empty())
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@ -173,4 +173,192 @@ namespace polysat {
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return true;
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}
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// TODO:
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// review translation from is_positive to ineq.strict
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/** Precondition: all variables other than v are assigned.
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*
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* \param[out] out_interval The forbidden interval for this constraint
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* \param[out] out_neg_cond Negation of the side condition (the side condition is true when the forbidden interval is trivial). May be NULL if the condition is constant.
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* \returns True iff a forbidden interval exists and the output parameters were set.
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*/
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bool forbidden_intervals::get_interval(solver& s, signed_constraint const& c, pvar v, eval_interval& out_interval, signed_constraint& out_neg_cond)
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{
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inequality ineq = c.as_inequality();
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// Current only works when degree(v) is at most one on both sides
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pdd lhs = ineq.lhs;
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pdd rhs = ineq.rhs;
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if (ineq.is_strict)
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swap(lhs, rhs);
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unsigned const deg1 = lhs.degree(v);
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unsigned const deg2 = rhs.degree(v);
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if (deg1 > 1 || deg2 > 1)
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return false;
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if (deg1 == 0 && deg2 == 0) {
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return false;
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UNREACHABLE(); // this case is not useful for conflict resolution (but it could be handled in principle)
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// i is empty or full, condition would be this constraint itself?
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return true;
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}
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unsigned const sz = s.size(v);
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dd::pdd_manager& m = s.sz2pdd(sz);
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rational const pow2 = rational::power_of_two(sz);
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rational const minus_one = pow2 - 1;
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pdd p1 = m.zero();
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pdd e1 = m.zero();
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if (deg1 == 0)
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e1 = lhs;
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else
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lhs.factor(v, 1, p1, e1);
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pdd p2 = m.zero();
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pdd e2 = m.zero();
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if (deg2 == 0)
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e2 = rhs;
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else
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rhs.factor(v, 1, p2, e2);
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// Interval extraction only works if v-coefficients are the same
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if (deg1 != 0 && deg2 != 0 && p1 != p2)
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return false;
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// Currently only works if coefficient is a power of two
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if (!p1.is_val())
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return false;
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if (!p2.is_val())
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return false;
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rational a1 = p1.val();
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rational a2 = p2.val();
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// TODO: to express the interval for coefficient 2^i symbolically, we need right-shift/upper-bits-extract in the language.
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// So currently we can only do it if the coefficient is 1 or -1.
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if (!a1.is_zero() && !a1.is_one() && a1 != minus_one)
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return false;
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if (!a2.is_zero() && !a2.is_one() && a2 != minus_one)
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return false;
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/*
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unsigned j1 = 0;
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unsigned j2 = 0;
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if (!a1.is_zero() && !a1.is_power_of_two(j1))
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return false;
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if (!a2.is_zero() && !a2.is_power_of_two(j2))
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return false;
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*/
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rational const y_coeff = a1.is_zero() ? a2 : a1;
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SASSERT(!y_coeff.is_zero());
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// Concrete values of evaluable terms
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auto e1s = e1.subst_val(s.assignment());
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auto e2s = e2.subst_val(s.assignment());
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// TODO: this is not always true! cjust[v]/conflict may contain unassigned variables (they're coming from a previous conflict, but together they lead to a conflict. need something else to handle that.)
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if (!e1s.is_val())
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return false;
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if (!e2s.is_val())
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return false;
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SASSERT(e1s.is_val());
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SASSERT(e2s.is_val());
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bool is_trivial;
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pdd condition_body = m.zero();
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pdd lo = m.zero();
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rational lo_val = rational::zero();
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pdd hi = m.zero();
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rational hi_val = rational::zero();
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if (a2.is_zero()) {
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SASSERT(!a1.is_zero());
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// e1 + t <= e2, with t = 2^j1*y
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// condition for empty/full: e2 == -1
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is_trivial = (e2s + 1).is_zero();
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condition_body = e2 + 1;
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if (!is_trivial) {
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lo = e2 - e1 + 1;
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lo_val = (e2s - e1s + 1).val();
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hi = -e1;
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hi_val = (-e1s).val();
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}
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}
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else if (a1.is_zero()) {
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SASSERT(!a2.is_zero());
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// e1 <= e2 + t, with t = 2^j2*y
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// condition for empty/full: e1 == 0
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is_trivial = e1s.is_zero();
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condition_body = e1;
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if (!is_trivial) {
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lo = -e2;
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lo_val = (-e2s).val();
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hi = e1 - e2;
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hi_val = (e1s - e2s).val();
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}
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}
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else {
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SASSERT(!a1.is_zero());
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SASSERT(!a2.is_zero());
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SASSERT_EQ(a1, a2);
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// e1 + t <= e2 + t, with t = 2^j1*y = 2^j2*y
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// condition for empty/full: e1 == e2
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is_trivial = e1s.val() == e2s.val();
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condition_body = e1 - e2;
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if (!is_trivial) {
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lo = -e2;
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lo_val = (-e2s).val();
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hi = -e1;
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hi_val = (-e1s).val();
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}
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}
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if (condition_body.is_val()) {
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// Condition is trivial; no need to create a constraint for that.
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SASSERT(is_trivial == condition_body.is_zero());
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out_neg_cond = nullptr;
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}
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else if (is_trivial)
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out_neg_cond = ~s.m_constraints.eq(0, condition_body);
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else
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out_neg_cond = s.m_constraints.eq(0, condition_body);
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if (is_trivial) {
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if (!ineq.is_strict)
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// TODO: we cannot use empty intervals for interpolation. So we
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// can remove the empty case (make it represent 'full' instead),
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// and return 'false' here. Then we do not need the proper/full
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// tag on intervals.
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out_interval = eval_interval::empty(m);
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else
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out_interval = eval_interval::full();
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}
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else {
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if (y_coeff == minus_one) {
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// Transform according to: y \in [l;u[ <=> -y \in [1-u;1-l[
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// -y \in [1-u;1-l[
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// <=> -y - (1 - u) < (1 - l) - (1 - u) { by: y \in [l;u[ <=> y - l < u - l }
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// <=> u - y - 1 < u - l { simplified }
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// <=> (u-l) - (u-y-1) - 1 < u-l { by: a < b <=> b - a - 1 < b }
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// <=> y - l < u - l { simplified }
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// <=> y \in [l;u[.
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lo = 1 - lo;
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hi = 1 - hi;
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swap(lo, hi);
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lo_val = mod(1 - lo_val, pow2);
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hi_val = mod(1 - hi_val, pow2);
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lo_val.swap(hi_val);
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}
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else
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SASSERT(y_coeff.is_one());
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if (ineq.is_strict) {
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swap(lo, hi);
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lo_val.swap(hi_val);
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}
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out_interval = eval_interval::proper(lo, lo_val, hi, hi_val);
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}
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return true;
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}
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}
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