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In mathematics, the empty set is the unique set having no elements; its size or cardinality (count of elements in a set) is zero. Some axiomatic set theories ensure that the empty set exists by including an axiom of empty set, while in other theories, its existence can be deduced. Many possible properties of sets are vacuously true for the empty set.
Any set other than the empty set is called non-empty.
In some textbooks and popularizations, the empty set is referred to as the "null set". However, null set is a distinct notion within the context of measure theory, in which it describes a set of measure zero (which is not necessarily empty). The empty set may also be called the void set.

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  1. O

    venting question - using old empty outdoor SVP as air vent

    Hi all, I have an old toilet on the top floor (to be removed) which empties into an outdoor vertical SVP and into the ground. The pipe is straight with a vent terminal on top. Another toilet on the ground floor empties through the suspended timber floor into (what I suspect) a drain. I wish...
  2. chloeradhsaw

    Gurgling Noise From Rad When System Drained F&E Empty And Boiler Off

    My heat only gas boiler is drained from the boiler drain valve - There is no water in the F&E tank. The hot water vented cylinder is removed. So far so good Twice this evening I heard radiator gurgling noises which frightened the life out of me I cant seem to reproduce the noise and I cant get...
  3. J

    What kind of pump can empty a full septic tank in a remote area?

    I thought I could buy an external pump to pull out with a two inch pipe and send it away from the house.
    • jcochr
    • Thread
    • america empty pump remote septic tank usa
    • Replies: 2
    • Forum: USA
  4. D

    Basin slow to empty

    Having a slight problem with the basin slow emptying. Plunnging it helps a little, i have taken the trap off and its clear, the pop up waste is clear, the waste runs into the internal soil stack, i think the issue is a flat run of the waste for about 2 meteres along the floor. I did ask the...
    • Deneva
    • Thread
    • america basin empty slow usa
    • Replies: 4
    • Forum: USA
  5. D

    When i empty sink water goes in toilet bowl

    When I empty the sink in my ensuite bathroom, the water goes into the toilet bowl. The toilet water when flushed comes up to the rim and slowly goes down. Some of the water comes up through the shower. All other toilets and sinks in the house are fine. The shower and bath in main bathroom are...
    • Debs
    • Thread
    • america bowl empty sink toilet usa water
    • Replies: 2
    • Forum: USA
  6. R

    Why did water empty out of my toilet bowl

    Last night I heard a gurgling noise coming from the toilet. Later when I lifted the lid I saw that all the water had emptied from the bowl.There looked like a powdery residue at the bottom, and there was powdery stains on the underside of the lid.I flushed and it filled up with water again. It...
    • richie51
    • Thread
    • america bowl empty toilet usa water
    • Replies: 6
    • Forum: USA
  7. O

    Cylinder runs empty ?!?!

    Customer: I have a non vented boiler system with a valiant Ecotech boiler and a NON valiant cylinder. The boiler has recently been serviced by valiant. The problem we have is that after half an hour the hot water runs out and then it takes another half an hour for it to get hot again. Has...
  8. N

    Empty tiger loop de-aerator

    Hi, oil ran out in June, got it refilled last week. I noticed the Afriso de-aerator did not fill up after pressing the burner reset button like it always has done. The installation is 18 years old. I suspected the Teddington fire valve and the inline oil filter, however I was able to pump 1.5...
  9. B

    HW Gas consumption for empty house ?

    Hi all, Bit of an odd question here. I've been on holiday and have the CH switched off, but did not stop the twice daily boost of HW on the timer. Given that here is no HW been consumed in the house when we are away I expected the gas consumption to be minimal as the loss from the 2 x uniSTOR...
  10. L

    Megaflow indirect hot water cylinder.

    Hi, have Megaflo indirect unvented cylinder heated by gas boiler. Have noticed that when mains water stopcock is closed I can still draw hot water from the cylinder. Is this normal or is there a problem with the cylinder?
    • LSJ
    • Thread
    • cylinder empty hot hot water hot water cylinder indirect megaflow running until water
    • Replies: 6
    • Forum: Plumbing Jobs | The Job-board
  11. AlexGas

    Always empty the pockets before using your washing machine...

    DOH! https://m.youtube.com/watch?v=M9GqlrSzuEw
  12. P

    ALERT! Bank account empty!

    Hi I just got a letter from Ray saying his website has been compromised. I just checked my account and it has been cleaned out. I urge you to check your accounts ASAP
  13. stani

    Rothenburger blue gas

    Has anyone else had problems with these cylinders leaking. I've had 2 recently used once taken burner off and when I've gone back next job I'm nearly on empty.
  14. B

    Is it safe to turn on my central heating with cold tank empty?

    All my upstairs water and hot water stopped working this morning. I checked and my cold water tank was empty. Via my insurance, an engineer called and tried replacing the value into the cold water tank but still no water came through. He diagnosed a blockage, probably limescale furring up the...
    • biterbit
    • Thread
    • about central central heating cold empty heating mains safe system tank turn on water
    • Replies: 22
    • Forum: Plumbing Jobs | The Job-board
  15. B

    Wanting to empty toilet cistern of water without turning off water.

    Hi people, I appreciate I may be wanting the impossible. I wish to replace the dual flush siphon in a toilet cistern. The toilet is quite old (possible 20 years old) and the siphon looks like it has been in there since then. The toilet has not been flushing properly and I am nearly certain it...
  16. R

    Empty Water Tank In Attic

    Hi All, i moved into a house a couple of years ago and have decided to board the loft. I've found any empty water tank that must have been used before an immersion tank was installed but it's still connected to a pipe going into the wall. Is it ok to remove the tank? If so, what should I do...
  17. U

    Empty loop on heating system

    Im having some work done on my shop. I had my heating system flushed through but I's sure that a loop feeding 1 radiator approx. 3 meters was left valved off and remains empty. is this likely to cause problems when the circuit is fully open and operational. thanks all
  18. J

    Frost Settings ISAR HE24

    My late mother in law’s bungalow is now empty and the insurance company have asked us to keep the heating on. There is a combi boiler (Ideal – Isar HE24) and a room thermostat in the hall. This I believe (looking at pictures of the stat and remote box) is a Honeywell Y6630D1007 but I cannot find...
  19. W

    Can I have air in boiler system from empty header tank...

    A while ago the inlet valve on the larger of 2 tanks in the loft seized up, this resulted in it emptying, (I noticed it only when there was no hot water). Recently I have has what I think is far more gurgling when the boiler is on, and sometimes you can hear water running into it when it has...
  20. A

    Glowworm Flexicom 30cx new pump needed-please help

    Hi, the condensate pump on my Flexicom 30cx has packed in (I'm pretty sure it is that as the reservoir fills within a day or so and if I empty it,it all works ok again for a day).Can I get a suitable pump that is not supplied by Glowworm (very expensive) and fit it myself?Money is tight just at...
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