There might possibly be times when you have an object that should 
only be held when another object is held. Normal locks can prevent
someone from picking something up a piece of radioactive waste
without lead gloves, but don't mind at all if you then drop the 

Luckily, the puzzle flag can help. If an object is set puzzle, then 
the player will be forced to drop that object if he ceases to pass
the object's lock. For example, if you have the above-mentioned
radioactive waste and lead gloves, you can type "@lock radioactive
waste=lead gloves", and then "@set radioactive waste=puzzle". It will 
be impossible to pick up the waste without the gloves, and if a 
player drops the lead gloves while carrying the radioactive waste, 
he/she will automatically drop the waste too.

[Read "help t-verbs" if you haven't. Otherwise, read "help t-programs".]