[0,1,2,3,4,5,7,8,9].combination(4){|x| puts x.join(" ") }
Standard input is empty
0 1 2 3 0 1 2 4 0 1 2 5 0 1 2 7 0 1 2 8 0 1 2 9 0 1 3 4 0 1 3 5 0 1 3 7 0 1 3 8 0 1 3 9 0 1 4 5 0 1 4 7 0 1 4 8 0 1 4 9 0 1 5 7 0 1 5 8 0 1 5 9 0 1 7 8 0 1 7 9 0 1 8 9 0 2 3 4 0 2 3 5 0 2 3 7 0 2 3 8 0 2 3 9 0 2 4 5 0 2 4 7 0 2 4 8 0 2 4 9 0 2 5 7 0 2 5 8 0 2 5 9 0 2 7 8 0 2 7 9 0 2 8 9 0 3 4 5 0 3 4 7 0 3 4 8 0 3 4 9 0 3 5 7 0 3 5 8 0 3 5 9 0 3 7 8 0 3 7 9 0 3 8 9 0 4 5 7 0 4 5 8 0 4 5 9 0 4 7 8 0 4 7 9 0 4 8 9 0 5 7 8 0 5 7 9 0 5 8 9 0 7 8 9 1 2 3 4 1 2 3 5 1 2 3 7 1 2 3 8 1 2 3 9 1 2 4 5 1 2 4 7 1 2 4 8 1 2 4 9 1 2 5 7 1 2 5 8 1 2 5 9 1 2 7 8 1 2 7 9 1 2 8 9 1 3 4 5 1 3 4 7 1 3 4 8 1 3 4 9 1 3 5 7 1 3 5 8 1 3 5 9 1 3 7 8 1 3 7 9 1 3 8 9 1 4 5 7 1 4 5 8 1 4 5 9 1 4 7 8 1 4 7 9 1 4 8 9 1 5 7 8 1 5 7 9 1 5 8 9 1 7 8 9 2 3 4 5 2 3 4 7 2 3 4 8 2 3 4 9 2 3 5 7 2 3 5 8 2 3 5 9 2 3 7 8 2 3 7 9 2 3 8 9 2 4 5 7 2 4 5 8 2 4 5 9 2 4 7 8 2 4 7 9 2 4 8 9 2 5 7 8 2 5 7 9 2 5 8 9 2 7 8 9 3 4 5 7 3 4 5 8 3 4 5 9 3 4 7 8 3 4 7 9 3 4 8 9 3 5 7 8 3 5 7 9 3 5 8 9 3 7 8 9 4 5 7 8 4 5 7 9 4 5 8 9 4 7 8 9 5 7 8 9