Fixed a few errors
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@ -178,7 +178,6 @@ Reduce the following expressions. \par
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\textbf{Solution for $(I~I)$:}\par
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Recall that $I = \lm x.x$. First, we rewrite the left $I$ to get $(\lm x . x )~I$. \par
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Applying this function by replacing $x$ with $I$, we get $I$:
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$$
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I ~ I =
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(\lm x . \tzm{b}x )~\tzm{a}I =
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@ -193,11 +192,7 @@ Reduce the following expressions. \par
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\draw[->,gray,shorten >=5pt,shorten <=3pt]
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(a.center) to (b.east);
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\end{tikzpicture}
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$$
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\vspace{0.5mm}
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So, $I~I$ reduces to itself. This makes sense, since the identity
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function doesn't change its input!
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$$\null
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\end{examplesolution}
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@ -214,11 +209,20 @@ Rewrite the following expressions with as few parentheses as possible, without c
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Remember that lambda calculus is left-associative.
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\vspace{2mm}
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\begin{itemize}[itemsep=2mm]
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\item $(\lm x. (\lm y. \lm (z. ((xz)(yz)))))$
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\item $(\lm x. (\lm y. \lm z. ((xz)(yz))))$
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\item $((ab)(cd))((ef)(gh))$
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\item $(\lm x. ((\lm y.(yx))(\lm v.v)z)u) (\lm w.w)$
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\end{itemize}
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\begin{solution}
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$(\lm x. ((\lm y.(yx))(\lm v.v)z)u) (\lm w.w) \implies (\lm x. (\lm y.yx) (\lm v.v)~z~u) \lm w.w$
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\vspace{2mm}
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It's important that a function's output (everything after the dot) will continue until we hit a close-paren.
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This is why we need the parentheses in the above example.
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\end{solution}
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\vfill
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\pagebreak
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@ -317,17 +321,18 @@ We've already seen this on the previous page: $K$ takes an input $x$ and uses it
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You can think of $K$ as a \say{factory} that constructs functions using the input we provide.
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\problem{}<firstcardinal>
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Let $C = \lm f. \Bigl[\lm g. \Bigl( \lm x. [~ g(f(x)) ~] \Bigr)\Bigr]$. For now, we'll call it the \say{composer.}
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Let $C = \lm f. \Bigl[\lm g. \Bigl( \lm x. [~ f(g(x)) ~] \Bigr)\Bigr]$. For now, we'll call it the \say{composer.} \par
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\note[Note]{We could also call $C$ the \say{right-associator.} Why?}
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\vspace{1mm}
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Note that $C$ has three \say{layers} of curry: it makes a function ($\lm g$) that makes another function ($\lm x$). \par
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$C$ has three \say{layers} of curry: it makes a function ($\lm g$) that makes another function ($\lm x$). \par
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If we look closely, we'll find that $C$ pretends to take three arguments.
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\vspace{1mm}
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What does $C$ do? Evaluate $(C~a~b~x)$ for arbitary expressions $a, b,$ and $x$. \par
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\hint{Place parentheses first. Remember, function application is left-associative.}
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\hint{Evaluate $(C~a)$ first. Remember, function application is left-associative.}
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\vfill
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