It will be convenient to adopt a notation (essentially one due to Dirac) according to which the elements of the Hilbert space – referred to as state vectors - are denoted by some symbol in an angled bracket, such as |ψ〉, |x〉, |φ〉, |l〉, |2〉, |3〉, |n 〉, |↑〉, |↓〉, |→〉, |↗), etc. Thus these symbols now denote quantum states.
