public bool Find(FreshVariable var, out object val)
{
if (IsEmpty())
{
val = null;
return(false);
}
if (Var == var)
{
val = Val;
return(true);
}
return(parent.Find(var, out val));
}
public Substitution Extend(FreshVariable var, object val)
{
return(new Substitution(this, var, val));
}
private Substitution(Substitution p, FreshVariable var, object val)
{
parent = p;
Var = var;
Val = val;
}