To prevent the splitting of votes among themselves, the TMC, Congress, AAP and RG can still unite even after they have declared their candidates by resorting to a strategic withdrawal of nominations in favour of the consensus candidate.
If the four opposition parties are going to field all 40 candidates, they can still zero in on only consensus candidates that too proportionately so as to get equitable representation.
160 candidates can then be narrowed down to 40 candidates. The reasoning is that suppose all the four opposition parties have a total vote share of 60%, then if they go separate ways, spitting of votes will hand the BJP with just 40% of the vote share the initiative, which should under no circumstances happen.
If each of the above parties have 20%, 20%, 15% and 5% vote share, they will be handing the BJP the initiative on a platter. Until today due to the anti-incumbency factor, a united opposition stands a distinct chance to win, but splitting of votes will definitely hand over the initiative to BJP.
The 120 candidates that withdraw can later be given their due by choosing them to head corporations and other plum post for their support. In this manner, the united opposition can come to power and surely defeat the BJP at the hustings.
