78 lines
2.3 KiB
Go
78 lines
2.3 KiB
Go
package recursion
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import (
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"logik/aussagenlogik/formulae"
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)
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/* ---------------------------------------------------------------- *
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* METHOD: compute NNF
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* ---------------------------------------------------------------- */
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// NOTE: diese bedarf einer Art Doppeltrekursion
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func NNF(tree formulae.Formula) formulae.Formula {
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// Definiere Schema:
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var schema = func(tree formulae.Formula, prevValues []formulae.FormulaPair) formulae.FormulaPair {
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// separate out positive and negative parts:
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var pairs = formulae.NewFormulaPairs(prevValues)
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var prevPos = pairs.Pos()
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var prevNeg = pairs.Neg()
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// compute value from previous positive/negative parts:
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if tree.IsPositiveLiteral() {
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return formulae.FormulaPair{
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Pos: tree.Deepcopy(),
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Neg: formulae.Negation(tree),
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}
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} else if tree.IsNegativeLiteral() {
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return formulae.FormulaPair{
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Pos: tree.Deepcopy(),
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Neg: prevPos[0],
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}
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} else if tree.IsTautologySymbol() {
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return formulae.FormulaPair{
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Pos: formulae.Tautology,
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Neg: formulae.Contradiction,
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}
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} else if tree.IsContradictionSymbol() {
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return formulae.FormulaPair{
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Pos: formulae.Contradiction,
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Neg: formulae.Tautology,
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}
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} else if tree.IsNegation() {
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return formulae.FormulaPair{
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Pos: prevNeg[0],
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Neg: prevPos[0],
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}
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} else if tree.IsConjunction2() {
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return formulae.FormulaPair{
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Pos: formulae.Conjunction2(prevPos[0], prevPos[1]),
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Neg: formulae.Disjunction2(prevNeg[0], prevNeg[1]),
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}
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} else if tree.IsConjunction() {
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return formulae.FormulaPair{
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Pos: formulae.Conjunction(prevPos),
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Neg: formulae.Disjunction(prevNeg),
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}
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} else if tree.IsDisjunction2() {
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return formulae.FormulaPair{
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Pos: formulae.Disjunction2(prevPos[0], prevPos[1]),
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Neg: formulae.Conjunction2(prevNeg[0], prevNeg[1]),
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}
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} else if tree.IsDisjunction() {
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return formulae.FormulaPair{
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Pos: formulae.Disjunction(prevPos),
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Neg: formulae.Conjunction(prevNeg),
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}
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} else if tree.IsImplication() {
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return formulae.FormulaPair{
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Pos: formulae.Implies(prevPos[0], prevPos[1]),
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Neg: formulae.Conjunction2(prevPos[0], prevNeg[1]),
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}
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} else {
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panic("Could not evaluate expression!")
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}
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}
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// Erzeuge Funktion aus Schema und berechne Wert:
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fn := formulae.CreateFromSchemeFmlPairValued(schema)
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return fn(tree).Pos
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}
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