A Regularity Test for Pushdown Machines by Stearns. Reg vs DPDA
On the succintness of different represenatsions of languages by Hartmanis. Reg, DPDA, Unambig CFL
Succintness of the complement and intersection of reg expressios by Gelade and Neven
Economy of descrption by automata, grammars, and formal systems by Meyer and Fischer
Complexity Measures for Regular Expressions by Ehrenfeuch and Zeiger
Succintness of Regular Expressions with Interleaving, Intersection and Counting by Gelade