data trts;
   do set =1 to 15;
   do trt=1 to 3;
   do rep=1 to 2;
   input unit $ @@;
   if unit='a' then y=12;
   if unit='b' then y=10;
   if unit='c' then y=11;
   if unit='d' then y=15;
   if unit='e' then y=14;
   if unit='f' then y=13;
   output;
   end; end; end;
cards;
a b c d e f
a b c e d f
a b c f d e
a c b d e f
a c b e d f
a c b f d e
a d b c e f
a d b e c f
a d b f c e
a e b c d f
a e b d c f
a e b f c d
a f b c d e
a f b d c e
a f b e c d