Calculation of the Limit

Pleas help to calculate the following limit

Limit[1/a*( p r (-\[Tau] + (1 - p r)^( a/\[Tau]) (\[Tau] - a Log[1 - p r])))/((-1 + p r) Log[ 1 - p r]^2),

What do you know about p, r and ?

Is that the initial form of the limit?

p, r and \tau are just positive parameters.