Here we look at a 3C response to 1NT used as 5-card Stayman. I nice modern addition to your bidding system. This in combination with a 2C Stayman response created an effective system for communication.
(522) NT Auctions: 2S Size Ask Response
(520) NT Auctions: Opponents' Doubles of Our Stayman and Transfers
(517) NT Auctions: 3S Minor Suit Slam Try After a 2NT Opening Bid
(503) Middle of the Hand Defense: Surround Plays and Power Shifts
(495) Advanced Card Play: Smother Play
(494) Advanced Card Play: Endplays
(484) Competitive Bidding: Leaping Michaels
(483) Competitive Bidding: Competing Over 2-Level Preempts - Lebensohl
(477) Defensive Carding: More Suit Preference
(475) Defensive Carding: Smith Echo (Reverse)
Against a NT contract, when the opponents win the first trick and attack another suit they are often leading their best suit. In this case, we have an opportunity to communicate with partner. Smith Echo is an agreement that makes use of this situation to tell partner if the opening lead was good or not.