sigma = ["a","b","c"]
1.upto(10) { |i|
    sigma.repeated_combination(i) { |a|
        ima = a.join
        1.upto(10) { |j|
            sigma.repeated_combination(j) { |b|
                imb = b.join
                if(!(ima =~  /aaa|bbb|ccc|aba|bab/) && !(imb =~ /aaa|bbb|ccc|aba|bab/))
                    puts "checking a->" + ima + " b->" + imb
                    #check(phi(tm, ima, imb))
                end
            }
        }
    }
}