Let us take several values of n:

**n = 1: **E_{1} = {(y_{1}) | y_{1} **R**}

Thus, E_{1} is just the set of real numbers, or the real line.
**n = 2: **E_{2} = {(y_{1}, y_{2}) | y_{i} **R**}

Thus, E_{2} is the set of pairs of real numbers, or the Cartesian plane.
**n = 3: **E_{3} = {(y_{1}, y_{2}, y_{3}) | y_{i} **R**}

Thus, E_{3} is the set of triples of real numbers, or three-dimensional Euclidean space.
**n = 4: **E_{4} = {(y_{1}, y_{2}, y_{3}, y_{4}) | y_{i} **R**}

Thus, E_{4} is the set of quadruples of real numbers, or four-dimensional Euclidean space.
etc., etc.

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