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2:27 AM
Hmm f=lambda n,s=" _":n*" "and f(n-1,"").join([s,"_"*(n-2)+"\n%c|%s|"%(64+n,"_"*n),""]) is 2 bytes longer, despite all the fluff
 
 
19 hours later…
9:33 PM
f=lambda n,s='  _':n and f(n-1,s)+"_"*(n-2)+"\n%c|%s|"%(64+n,"_"*n)+f(n-1,'')or s
pushing the start string along the left branch
 

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