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Discussion of Problem 1265. Mirror

Warning and Test 5
Posted by Igor Parfenov 2 Jun 2023 02:40
Do not believe the simplicity of the task at first glance. This is NOT a geometry problem. This is a "precision" problem.

Also, I misunderstood problem a little. If the second point is in front of mirror, but can not be seen in it, it is INVISIBLE. It is checked in test 5.

Input
7 2
5 3
1 3
4 4

Output
INVISIBLE