[blml] Obviously this is the prime duty

[David Burn]

"If only you did not so often try to be clever, you would not so often end
up looking foolish."

Victor Mollo

[TWM]

So, my little bird-brained friend, you will discover that passing 2H is not
a logical alternative for a person who has become aware of the actual
vulnerability.  You may delete all knowledge of his partner saying "15-17"
from his memory if you wish - but what you cannot, and may not, delete is
the knowledge he received from looking up and seeing the RED band on his
side of the board.

[DALB]

>From the footnote to Law 75, mutatis mutandis:

In both cases [South's bid is correct, North's explanation wrong; South's
bid is wrong, North's explanation correct] South, having heard North's
explanation, knows that his own 1NT bid has been misinterpreted. This
knowledge is "unauthorised information'' (see Law 16A), so South must be
careful not to base subsequent actions on this information (if he does, the
Director shall award an adjusted score). For instance, if North responds two
hearts, South has the unauthorised information that this bid shows a spade
suit; but South's responsibility is to act as though North had made a
natural and non-forcing bid of two hearts.

David Burn
London, England