Take care with this. If the elements of an array are themselves arrays then you cannot remove them in this way. For example:
_posA = getPos a
_posB = getPos b
_posC = getPos c
_positions = [_posA,_posB,_posC]
Then the line:
_positions = _positions - [_posA]
will do nothing.
So I would have to go about it as so:
_posA = getPos a
_posB = getPos b
_posC = getPos c
_positions = [_posA,_posB,_posC]
_myvar = _positions select 0
_positions = _positions - _myvar -->> _positions = [_posB,_posC]