Level  11 is not solvable -- needs 2 more emeralds
Level  18 is not solvable -- spaceships always either bunch up (2 die at once + blow up an emerald) or get stuck in an infinite loop (one emerald is never accessible)
Level  49 is not solvable -- can barely move at all
Level  56 is not solvable -- needs 4 dynamites (tree, green key, bomb inside walls, and to escape after getting the last emerald); only provides 3
Level  76 is not solvable -- has no exit!
