The Twelvefold Way in Combinatorics

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Questions and Answers

In the twelvefold way in combinatorics, what is the general problem that is considered?

  • Enumeration of equivalence classes of functions (correct)
  • Counting permutations and combinations
  • Enumeration of subsets
  • Classification of finite sets

What does it mean when a function f is injective?

  • Each b in X may occur multiple times in the image of f
  • Each a in N may be sent by f to any b in X
  • Each value for a in N must be distinct from every other (correct)
  • There must be at least one a in N such that f(a) = b for each b in X

What is the condition for a function to be surjective?

  • Each a in N may be sent by f to any b in X
  • For each b in X there must be at least one a in N such that f(a) = b (correct)
  • Each b in X may occur multiple times in the image of f
  • Each value for a in N must be distinct from every other

When is 'f is bijective' considered as an option?

<p>When there are equal cardinalities of two finite sets, n = x (B)</p> Signup and view all the answers

What does 'No condition' imply for the function f?

<p>Each value for a in N may be sent by f to any b in X (D)</p> Signup and view all the answers

Which mathematician is credited with the idea of the classification known as the twelvefold way?

<p>Gian-Carlo Rota (B)</p> Signup and view all the answers

In how many ways can the three conditions on the functions and the four equivalence relations be paired?

<p>12 (D)</p> Signup and view all the answers

Which of the following is equivalent to counting n-permutations of X?

<p>Counting injective functions N → X up to permutations of N (A)</p> Signup and view all the answers

What does counting n-combinations of X correspond to?

<p>Counting all functions N → X up to permutations of N (C)</p> Signup and view all the answers

When n = x, counting permutations of the set X is equivalent to counting:

<p>Injective functions N → X up to permutations of N (A)</p> Signup and view all the answers

What is equivalent to counting partitions of the set N into x subsets?

<p>Counting all surjective functions N → X up to permutations of X (C)</p> Signup and view all the answers

What does counting compositions of the number n into x parts correspond to?

<p>Counting all surjective functions N → X up to permutations of N (D)</p> Signup and view all the answers

What is reflected by the property that any ball can go into only one box?

<p>Injective function (D)</p> Signup and view all the answers

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