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read(positions) superposition
replace positions with their index in the input superposition
if the input is a sequence, then apply this operator for each sub-superposition
index values start from 1, not 0
negative values are also valid, so -1 is last element, -2 is second last element, etc
if out of range, or not a number, return |> for that slot

-- a simple abstract example:
read(|1> + |3> + |5>) (|one> + |two> + |three> + |four> + |five> + |six> + |seven>)
    |one> + |three> + |five>

-- negative indices example:
read(|-1> + |-3> + |-5>) (|one> + |two> + |three> + |four> + |five> + |six> + |seven>)
    |seven> + |five> + |three>

-- if out of range, or not a number, return |> for that slot:
read(|1> + |fish> + |11> + |4>) (|one> + |two> + |three> + |four> + |five> + |six> + |seven>)
    |one> + |four>