"OR" was just my (bad) way to explain it. In plain English: if isInteger(x) is true, x is definitely a `number` if isInteger(x) is false, x is unknown/unalter

"OR" was just my (bad) way to explain it. In plain English: if isInteger(x) is true, x is definitely a `number` if isInteger(x) is false, x is unknown/unaltered (it remains `typeof x`) Current type guards can't express "yes versus maybe", so isInteger cannot be a type guard at all.