Decomposing into 2NF
Keep the simple dependencies as is:

b -&gt; f
d -&gt; e


Remove the dependent columns from the other dependencies.

a -&gt; b,c,d 
b,c -&gt; a,d 


At this point you have two candidate keys a and b,c.  As we already have a dependency on b.  I would keep the b,c dependency and drop the dependency on a.  It would appear that b,c defines a weak entity (or repeating group) related to b.  I would consider creating a unique key on a.