sysuse nlsw88, clear gen hs = grade == 12 if grade < . gen sc = grade > 12 & grade < 16 if grade < . gen c = grade >= 16 if grade < . gen lnwage = ln(wage) gen tenure2 = tenure^2 gen white = race == 1 if race < . propcnsreg lnwage white tenure tenure2 union, /// lambda(tenure white) /// constrained(hs sc c) mimic