Formation of toluene from (cyclobutane-1,2,3-triyl)trimethanol using conc. sulphuric acid
Seeing the reaction given here, I assume that is an on-paper reaction that takes place and that all three alcoholic groups are dehydrated.



The mechanism (on paper) seems to be as follows
Dehydration $1$
For the first dehydration, the carbocation formed is stabilised via ring expansion and then forms a double bond as follows:



Dehydration $2$
Similar to the first dehydration, a ring expansion occurs to stabilize the carbocation by forming a 6-member ring:



Dehydration $3$
In the third dehydration, a hydride shift takes place concomitantly forming a tertiary carbocation stabilized by conjugation with the double bonds. The double bond is then formed giving the compound aromaticity.