1C

Forcing

Opener has about 5 or fewer losers, and one of:

Responses

There are 3 negative and 1 semi-positive responses; positive responses show 3 or more controls by steps, and are forcing to game.

1D
0-5HCP
1H
6+HCP, < 3 Controls; forcing to 2NT

Semi-positive hands receive very similar treatment to positive hands, but not all sequences are forcing to game.

1S
3 Controls
1NT
4 Controls
2C
5 Controls
2D
6 Controls
2H|S
0-5HCP, 6+card major with 2 honours, no better than KJxxxx
2NT
7 Controls

Intervention

1 D|H|S
Pass
Replaces 1D
Double
Replaces 1H
1 NT
Pass
Replaces 1D
Double
6+HCP
Suit
Pass
Nothing more to say
Double
For penalties
2 NT
3-4 Controls
Cue bid
5+ Controls
New suit
Natural, forcing
Suit
Weak and non-forcing
2C|D|H|S
Pass
< 3 Controls
Double
Penalties
2NT
3-4 Controls
New Suit
Natural, forcing
2NT+
Pass
Negative
Double
Optional, 7+ points with no good suit
New Suit
Natural, forcing, but may just be a moderate 6 card suit.
Double
Pass
0-3 points
Redouble
3-5HCP, values in Clubs
1D
4-5HCP
1H
6+HCP, < 3 Controls
Other
Further responses retain their original character.