Let x,y ∈ R satisfy
x < y. Prove that there exists a q ∈
Q such that x < q <
y.
Strategy for solving the problem
Show that there exists an n ∈
N+ such that 0 < 1/n <
y - x.
Letting A = {k : Z |
k < ny}, where Z denotes the
set of all integers, show that A is a non-empty subset of
R with an upper bound in R.
(Hint: Use...