Weissberger 
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After the Stayman rebid of 2D denying a four card major, a rebid by
responder of 3D is used to show either
  1) a game-going or invitational hand with 5-5 in the majors
  2) a game-going hand with 5 spades and 4 hearts

With a game-going hand with 5 hearts and 4 spades, responder bids 
3H over the opening 1NT (hoping that opener bids 3S with 4 of them).

Opener then rebids with 3 spades either 3S with a minimum or 4S 
with a maximum.  Without 3 spades, opener rebids 3H with a minimum
or 3NT with a maximum.  Over 3NT, if responder has the game-forcing
hand and 5-5 in the majors, responder may bid 4D to request opener
to bid 4H.