#043 Locking/Unlocking a door

Have you ever encountered situations where you want to lock or unlock a door, but got confused about turning the key clockwise or anti-clockwise?

And that is when you try your luck, try turning clockwise... you heard a sound *CLICK*, but the door won't open. "damn it, I double locked it..." After realising your silly mistake, you quickly turn anticlockwise to double unlock the door. But after the *CLICK* sound, you manage to open the door before hearing the second *CLICK*.
At this moment, some people may just enter the room and forget about all this door issue, and someday this stupid mistake will come and haunt him/her again.
Whereas some people will quickly realise that the door was not lock in the first place, and for the past 30 seconds he/she had totally wasted his/her precious time to lock and unlock the door before entering.

Well, I have a solution to solve this problem! Just memorise the direction to unlock every single door that you have ever encountered.
Okay, this is too difficult for most people and the problem will still occur when one encounters a door for the first time.

Another possible solution.
When you want to enter a door:
First, try opening it. Sometime it is not locked and this problem will not happen at all.
If it is proven to be locked, this is where my theorem comes in.
"Turning the key in clockwise direction unlocks the door if and only if the door knob/handle is on the left of the door."
Of course, there are several other version of this theorem, like
"Turning the key in anti-clockwise direction unlocks the door if and only if the door knob/handle is on the right of the door." Or,
"Turning the key in anti-clockwise direction locks the door if and only if the door knob/handle is on the left of the door." etc...

The proof is rather complicated and it is omitted in this blog.

If memorising this theorem is still too troublesome, I have a corollary which will make life much easier.
But first, one must know that the 'lock thing' which locks the door to the door frame is extended out from the door. So to unlock a door, what you need to do is to make this metal 'lock thing' retract back into the door.
When you insert the key, assuming that the original position is vertical (if it is horizontal, simply turn clockwise or anti-clockwise to position it vertical), take the top of the key to be the 'mark'.
The corollary is "the 'lock thing' will move in the same direction as the 'mark'." e.g. If you want the 'lock thing' to move left, move the 'mark' to the left, which is turning the key in the anti-clockwise direction.
Some may feel a little confused about what I am trying to say, but just give some time to think and picture about the direction to turn the key, one will see that this corollary is exactly talking about the same thing as the theorem.

I personally use this corollary rather than the theorem because it avoids all the terms clockwise/anti-clockwise, lock/unlock or left/right of the door. Which causes fatal mistake when just one term is memorised wrongly. With this corollary, one will easily apply it to locking/unlocking a door with door knob on the left/right.

This may not be an earthshaking finding or theorem that will benefit the economic or whatever. But with this small knowledge, thousands and thousands of people can each save a few seconds every time they unlock/lock for the rest of their lives.

Before I conclude this post, let me restate the corollary once again.
"The 'lock thing' will move in the same direction as the 'mark'."

Thank you and hope everyone enjoy unlocking/locking a door next time.


~milkteaisthebest~