Negative Double

     

                    Over any other 1-level opening, followed by intervention, negative double are used. If in place of a negative double your partner makes a bid in an unbid denomination AT THE SAME LEVEL then this will be 5+ card suit - this is to be taken seriously although not actually forcing  - except at the one-level!
If this bid fits well along with partner's opening bid and your response, he will take positive action.