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{\bf Mathematical Logic, WS 2018.
Homework 9, given Jan 15, due Jan. 22.}

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\noindent
Use the following equalities in order to compute $L[\langle a, b, c \rangle]$
by substitution and replacement:
$$ L[\langle \rangle] = 0,\ \ 
L[X \smile \langle x \rangle] = L[X] + 1.$$
Construct the tail recursive function which can be used for the computation of
L and prove the respective equality.
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