Features of Acol (English Bridge version):

• openings with 4+ cards (NT rebid shows 15+ HCP):

  • • 5332, 4333 and 4432 - 15+ HCP;

    • 54xx, 6xxx or better, 10+ HCP;

    • 4441, 4414, 4144 and 1444 - 12+ HCP,

• weak 1NT opening 12-14 HCP, 5332 or 4432 or 4333.

The weak notrump effect on natural sequences:

1♣ - 1♦

?

1N - a weak notrump should show 15-16 HCP (normally shows 12-14 HCP);

2N - 17-18 HCP;

2N - 19-20 HCP;

• 2♣ - 22+ HCP on any hand;

• 2N - 20-22 HCP,  balanced hand;

• weak two openers.

Responses after 1NT's weak opening:

• 2♣ - weak Stayman:

  • • 0-10 HCP, 6+♣;

    • 0-10 HCP, 5+♦, 3+♥, 3+♠;

    • 9-10 HCP, 5+M, 3+OM;

    • 11+HCP, 4+M,

• 2♦, 2♥, 2♠ - five to pass;

• 2N - 11-12 HCP, bal;

• 3♣, 3♦, 3♥, 3♠ - 5+ GF;

• 3N - 12+HCP, bal;

• 4♣ - Gerber;

• 4♦, 4♥, 4♠ - to play;

• 4N - Quantitative 4NT;

• 5N - 5NT pick a slam.