options ls=65 ps=50;
data a;
input y period trt subject restrt @@;
datalines;
16 1 1 1 0    19 1 2 2 0    23 1 3 3 0    17 1 4 4 0
23 2 2 1 1    18 2 3 2 2    12 2 4 3 3    28 2 1 4 4
24 3 4 1 2    26 3 1 2 3    25 3 2 3 4    21 3 3 4 1
15 4 3 1 4    17 4 4 2 1    19 4 1 3 2    20 4 2 4 3
;
run;
proc glm;
class period trt subject restrt;
model y=period trt subject restrt/solution e;
/* lack of balance in restrt means Treatment means are not estimable */
lsmeans trt restrt;
run;

proc glimmix plots=all;
class period trt subject restrt;
model y=period trt subject restrt/solution;
/* lack of balance in restrt means Treatment means are not estimable */
/* Differences are estimable, but no graphic is produced. */
lsmeans trt restrt/pdiff adjust=tukey cl; 
run;