Tricky 30 ("The Crankshaft"), no more than 1 skill per lemming
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Because you can't climb and mine as in the standard solution, your only alternative
is to use builders to get up onto the pillars.  Due to the time limit and the
inability to multitask (again, because you can't climb), you need to use as few
builders as possible to get up onto the pillars (so that it doesn't take too much 
time), which is 4 builders if you start building from the edge of the mining tunnel.
To allow lemmings from the crowd to get back up while the bridge is in progress, 
you need a second mining tunnel, and a bridge that goes over the top of that tunnel.
The result is what you see in the screenshot.

One more detail:  the fall becomes fatal during the last of the 4 builders needed to
get up onto the pillar, so before you start that, you need to block off the crowd 
both above/left, and below/right, and free the blockers once the bridge is near 
completion by using exploders from the crowd.  This is the reason for the explosion 
pits you see in the screenshot.

There are 2 pillars that require you to use this procedure to get up onto, so you end
up using all 10 builders, and only 4 exploders (you can lose 8 in this level).  The 
procedure for a single pillar takes about 1.5 minutes, so even having to do it twice, 
you still have about 1 minute left, enough to complete the level in DOS Lemmings.
