options ls=80;
data bodyfat;
input x1 x2 x3 y;
datalines;
19.5  43.1  29.1  11.9
  24.7  49.8  28.2  22.8
  30.7  51.9  37.0  18.7
  29.8  54.3  31.1  20.1
  19.1  42.2  30.9  12.9
  25.6  53.9  23.7  21.7
  31.4  58.5  27.6  27.1
  27.9  52.1  30.6  25.4
  22.1  49.9  23.2  21.3
  25.5  53.5  24.8  19.3
  31.1  56.6  30.0  25.4
  30.4  56.7  28.3  27.2
  18.7  46.5  23.0  11.7
  19.7  44.2  28.6  17.8
  14.6  42.7  21.3  12.8
  29.5  54.4  30.1  23.9
  27.7  55.3  25.7  22.6
  30.2  58.6  24.6  25.4
  22.7  48.2  27.1  14.8
  25.2  51.0  27.5  21.1
;

proc reg data=bodyfat;
 model y=x1;
 model y=x2;
 model y=x1 x2;
 model y=x1 x2 x3;
 model y=x1 x3;

proc reg data=bodyfat;
  model y= x1 x2 x3/ss1 ss2;

proc reg data=bodyfat;
  model y= x1 x3 x2/ss1 ss2;   

proc reg data=bodyfat;
  model y= x3 x2 x1/ss1 ss2;   
test1: test x3=0;
test2: test x2=0,x3=0;
test3: test x2,x3;
/* test2 and test3 are equivalent*/
test4: test x1=4;
test5: test x2=x3;

data bodyfat;set bodyfat;
xnew=x2+x3;

proc reg data=bodyfat;
 model y=x1 xnew; 


data bodyfat;set bodyfat;
ynew=y-4*x1;

proc reg data=bodyfat;
  model ynew=x2 x3;
run;