Whew, hard to come up with a good topic name for this one. Say every level gave you 8 of each skill. Now, out of these 64 skills available, you can only use 8. How many levels can you solve, with how many of each skill?
Now you get unlimited skills! Let's try to find all the possible combos of different skills, with the smallest numbers for each.!
Just Dig/Ozone friendly lemmings (works for both):
1 basher
1 digger
1 miner
4 bombers