  Recently, a careful canonical quantisation of the theory of closed bosonic
tensionless strings has resulted in the discovery of three separate vacua and
hence three different quantum theories that emerge from this single classical
tensionless theory. In this note, we perform lightcone quantisation with the
aim of determination of the critical dimension of these three inequivalent
quantum theories. The satisfying conclusion of a rather long and tedious
calculation is that one of vacua does not lead to any constraint on the number
of dimensions, while the other two give $D=26$. This implies that all three
quantum tensionless theories can be thought of as consistent sub-sectors of
quantum tensile bosonic closed string theory.
