why loop is not valid and this is valid

Because rule from Kata description says:

Sometimes a line may be valid in one direction but not the other. Such a line is still considered valid.

Because the loop is ambiguous from BOTH ends. This line is ambiguous from only ONE end. Therefore it is "valid".

good point

ohh, now it makes sense

That one is only ambiguous if you start from the left X.

But the Kata description says:

Sometimes a line may be valid in one direction but not the other. Such a line is still considered valid.

     +-------+          
     |      +++---+     
  X--+      +-+   X  

ex good #5

on 4th + it has a choice, whether to go left or right, its ambiguous, shouldn't it be false?

Your understanding is correct.

lift rule #6
"When called, the Lift will stop at a floor even if it is full, although unless somebody gets off nobody else can get on!"

I'm confused with this rule, what i understood is when the lift is full it will stop at floor even though no one can get in, although they could have get in if lift wasn't full. Am I correct or wrong, please help.

:-)

Took me 6 hours to figure out an algorithm for this kata and i finnaly did it, i must say it was quite an adventure.