public Substitution MUnify(AccessibilityRelation relation, Formula formula)
{
var unif = Unify(formula);
var eta = relation.WorldUnify(WorldIndex, formula.WorldIndex);
unif.Compose(eta);
return(unif);
}
public Substitution WorldUnify(AccessibilityRelation relation, WorldIndex i, WorldIndex j)
{
//2b -> one is ground and the other world variable
if (i.EndSymbol.IsGround || j.EndSymbol.IsGround)
{
//Need to verify if n is accessible from the parent of w
var n = i.EndSymbol.IsGround ? i.EndSymbol : j.EndSymbol;
var w = !i.EndSymbol.IsGround ? i.EndSymbol : j.EndSymbol;
if (relation.Contains(w.ParentSymbol, n))
{
var sub = new Substitution();
sub.Add(n, w);
return(sub);
}
return(null);
}
//2c -> both are world variables
else
{
//(i)
if (relation.Contains(i.EndSymbol.ParentSymbol, j.EndSymbol) || relation.Contains(j.EndSymbol.ParentSymbol, i.EndSymbol))
{
return(new Substitution(i.EndSymbol, j.EndSymbol));
}
//(ii)
else
{
var parentUnification = relation.WorldUnify(i.ParentIndex, j.ParentIndex);
if (parentUnification == null)
{
return(null);
}
else
{
new Substitution(i.EndSymbol, j.EndSymbol).Compose(parentUnification);
return(parentUnification);
}
}
}
}