"so, assuming the declared fact "x = y", whenever you see "x" you could substitute "y" (and vice versa), and it would make no difference whatsoever?" In mathem

"so, assuming the declared fact "x = y", whenever you see "x" you could substitute "y" (and vice versa), and it would make no difference whatsoever?" In mathematics, yes. That is the entire point of the '=' statement.