var
s:set of 1..4;
s:=[];
a:=RandomFrom([1,2,3,4]);
s:=s+[a];
repeat
b:=RandomFrom([1,2,3,4]);
undilt not (b in s);
s:=s+[b];
repeat
c:=RandomFrom([1,2,3,4]);
undilt not (c in s);
s:=s+[c];
repeat
d:=RandomFrom([1,2,3,4]);
undilt not (d in s);
s:=s+[b];