[0,1,2,4,6,7,8,9].combination(3){|x| puts x.join(" ") }
Standard input is empty
0 1 2 0 1 4 0 1 6 0 1 7 0 1 8 0 1 9 0 2 4 0 2 6 0 2 7 0 2 8 0 2 9 0 4 6 0 4 7 0 4 8 0 4 9 0 6 7 0 6 8 0 6 9 0 7 8 0 7 9 0 8 9 1 2 4 1 2 6 1 2 7 1 2 8 1 2 9 1 4 6 1 4 7 1 4 8 1 4 9 1 6 7 1 6 8 1 6 9 1 7 8 1 7 9 1 8 9 2 4 6 2 4 7 2 4 8 2 4 9 2 6 7 2 6 8 2 6 9 2 7 8 2 7 9 2 8 9 4 6 7 4 6 8 4 6 9 4 7 8 4 7 9 4 8 9 6 7 8 6 7 9 6 8 9 7 8 9