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Problem 2.5

10 十一月, 2015 - 10:27

To which of the following statements can the transfer principle be applied? If you think it can't be applied to a certain statement, try to prove that the statement is false for the hyperreals, e.g., by giving a counterexample.

  1. For any real numbers x and yx+y=y+x.
  2. The sine of any real number is between -1 and 1.
  3. For any real number x, there exists another real number y that is greater than x.
  4. For any real numbers x\neq y, there exists another real number z such that x<z<y.
  5. For any real numbers x\neq y, there exists a rational number z such that x<z<y. (A rational number is one that can be expressed as an integer divided by another integer.)
  6. For any real numbers xy, and z(x+y)+z=x+(y+z).
  7. For any real numbers x and y, either x<y or x=y or x>y
  8. For any real number xx+1\neq x.  

Solutions for chapter 2