public override BooleanExp Replace(BooleanExp exp, char c) { throw new NotImplementedException(); }
public abstract BooleanExp Replace(BooleanExp exp, char c);
public AndExpression(BooleanExp op1, BooleanExp op2) { _operand1 = op1; _operand2 = op2; }
public NotExpression(BooleanExp exp) { this.exp = exp; }