description:
drop-above[t] sp
ie, drop all kets with coeff > t from the given superposition
examples:
drop-above[2] (- |a> + 0|b> + |c> + 2|d> + 3|e> + 4|f>)
- |a> + 0|b> + |c> + 2|d>
see also:
drop, drop-above, sdrop