Question: > 
> There is a group of finite aliens on a spaceship. Show that there are at least $2$ aliens who know the same number of aliens on the spaceship. 
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I was given a hint, and that was to use the pigeonhole principle. I think I can visually see it but I am unsure how to show it.

Answer: 
**Hint:**

There are $N$ aliens, and assume one of the alien knows $K$ aliens. $(N>K)$

Can each alien know **distinct** number of aliens? 

Assume $A\_1$ knows ${A\_2,A\_3 \dots A\_{K+1}}$, now that $A\_2$ knows $K$ aliens, the aliens who he knows also knows him.(Though confusing, its the fact -evil laugh-)
suppose there are 10 aliens for example .
alien 1 knows alien 2 , how many aliens does 2 know now ?? for the hypothesis to be false alien 2 already knows alien 1 and for him not to know just 1 lets assume he knows alien 3 thus knows 2 .
same for alien 3 , he must know 3 .. continueing onward when we get to alien 10 he knows 10 aliens but since he cant count himself thats a contradiction hence 2 aliens know same number of aliens .