Illustration of initial terms of A058759.

We wish to realize the Boolean function f(X_1, ..., X_n)
with a two-terminal network
using AND's and OR's applied to the variables X_1, X_1',
..., X_n, X_n'. What we count is the total number
of times the variables X_1, X_1', ..., X_n, X_n' are used.

Conventions:
------------

o------o  means 0 or FALSE or CLOSED

o-    -o  means 1 or TRUE or OPEN

prime means "NOT"

o--- X --- Y ---o is X + Y = X OR Y

    
     X
    / \
o--o   o--o   is XY = X AND Y
    \ /
     Y

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For n=1 the worst case is f = X, circuit is

         o---- X ----o

requiring 1 variable.

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For n=2 the worst case is f = X XOR Y, circuit is


         X   X'
        / \ / \
    o--o   o   o---o
        \ / \ /
         Y'  Y 

requiring 4 uses of the variables

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For n=3 the worst is X XOR Y XOR Z, circuit is

      o-- Y --o
     / \     / \
    X   Y'  /   Z
   /     \ /     \
o-o       \       o-o
   \     / \     /
    X'  Y'  \   Z'
     \ /     \ /
      o-- Y --o

requiring 8 uses of the variables.

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