Landy convention
Landy, named after its inventor Alvin Landy, is the first of several conventional defenses created to compete against an opponent's one notrump opening. Landy is a 2 overcall of the opponents' 1NT opening to show at least four cards in each of the major suits; all other bids are natural. Requirements for the overcall vary from partnership to partnership: some require 5-5, some 5-4, and yet others only 4-4. The partner can take a preference to either major or make a non-forcing bid of a suit; 2NT is used as a forcing query.
Extended Landy
An extension was proposed by Ira Rubin in 1947 using 2 as a takeout request after a response or rebid of 1NT after a suit opening. It implies more distribution and less strength than a double. It also applies in the passout seat.Based on his initial inability to overcall the 1 opening directly, the bid of 2 by North shows five or more clubs and exactly four hearts. Similar uses were developed later by others.
Variations
Various additional modifications to Landy have appeared over years, by various authors. The original Landy convention is deemed obsolete amongst tournament players today in favor of more advanced conventions. It is still very popular at club level.Multi-Landy
A particular popular modification in the Netherlands is Multi-Landy, a combination of Landy, the Multi 2 diamonds convention and the Muiderberg convention. In this modification, the 2 overcall is the same as in Landy, the 2 overcall shows a 6-card major suit, and 2 or 2 overcall shows five cards in that major suit and at least four cards in a minor suit.Very similar is Reverse or Modified Cappelletti, the only difference being that the 2 overcall shows any 6-card suit, either a minor or a major.