ket1 .. ket2
return the value of range(ket1, ket2)
ie, return the superposition of ket1, ket1 + 1, ket1 + 2, ... , ket2
we do our best to preserve categories
if you require step size other than 1, then you need to use the range(start, stop, step) function
note, the result is a superposition, not a sequence
if you require a sequence, either use sp2seq or srange()
if the kets are 2D then return a corresponding 2D patch
if ket2 is less than ket1, return the empty ket