I have seen . used as multiplication rather than * (notation varies according to locale). That .1 is a *1, so the 1 can be removed from the final result.

>> z^0 becomes point one (.1).

y^(-4)z^0 becomes y^(-4)*(1) = y^(-4) = 1/y^4

>> z^0 becomes point one (.1).

y^(-4)z^0 becomes y^(-4)*(1) = y^(-4) = 1/y^4