<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _compute(self, approx):
 """ Deletion-based MUS extraction. Given an over-approximation of an MUS, i.e. an unsatisfiable core previously returned by a SAT oracle, the method represents a loop, which at each iteration removes a clause from the core and checks whether the remaining clauses of the approximation are unsatisfiable together with the hard clauses. Soft clauses are (de)activated using the standard MiniSat-like assumptions interface [2]_. Each soft clause :math:`c` is augmented with a selector literal :math:`s`, e.g. :math:`(c) \gets (c \\vee \\neg{s})`. As a result, clause :math:`c` can be activated by assuming literal :math:`s`. The over-approximation provided as an input is specified as a list of selector literals for clauses in the unsatisfiable core. .. [2] Niklas Eén, Niklas Sörensson. *Temporal induction by incremental SAT solving*. Electr. Notes Theor. Comput. Sci. 89(4). 2003. pp. 543-560 :param approx: an over-approximation of an MUS :type approx: list(int) Note that the method does not return. Instead, after its execution, the input over-approximation is refined and contains an MUS. """


        i = 0

        while i < len(approx):
            to_test = approx[:i] + approx[(i + 1):]
            sel, clid = approx[i], self.vmap[approx[i]]

            if self.verbose > 1:
                print('c testing clid: {0}'.format(clid), end='')

            if self.oracle.solve(assumptions=to_test):
                if self.verbose > 1:
                    print(' -> sat (keeping {0})'.format(clid))

                i += 1
            else:
                if self.verbose > 1:
                    print(' -> unsat (removing {0})'.format(clid))

                approx = to_test