By using Riemann--Hilbert problem based techniques, we obtain the asymptotic
expansion of lacunary Toeplitz determinants detN[cℓa−mb[f]] generated by holomorhpic symbols, where ℓa=a (resp. mb=b)
except for a finite subset of indices a=h1,…,hn (resp. b=t1,…,tr). In addition to the usual Szeg\"{o} asymptotics, our answer involves a
determinant of size n+r.Comment: 11 page