protected virtual bool TestEquals(ConstantFormulaTree other)
 {
     return(true);
 }
 protected override bool TestEquals(ConstantFormulaTree other)
 {
     return base.TestEquals(other) && TestEquals((FormulaNodeVariable) other);
 }
 protected override bool TestEquals(ConstantFormulaTree other)
 {
     return(base.TestEquals(other) && TestEquals((FormulaNodeVariable)other));
 }