Merge branch 'master' of ssh://server.philosophy.fas.nyu.edu/Users/lambda/lambda
[lambda.git] / hints / assignment_4_hint_4.mdwn
1 Hints for Y1,Y2. 
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3 *       Begin by trying to define `X1` and `X2` directly, then once they're working, you can abstract back to a pair of combinators `Y1` and `Y2` that generate `X1` and `X2` for a given pair of arguments `T1` and `T2`.
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5         You want:
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7                 X1 <~~> T1 X1 X2 and
8                 X2 <~~> T2 X1 X2
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10 *       X1 is presumably going to have some form like:
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12                 (\elem1 elem2 ... (T1
13                                                         (do-something-with-the-elems-to-make-X1)
14                                                         (do-something-with-the-elems-to-make-X2)
15                                                   ))
16                 some-elem1 some-elem2 ...
17         
18         Right? What will the form of X2 be?
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20 *       Can you see how to go on?
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22 *       Call the displayed abstract above `(\elem1 elem2 ... (...))` "elem0". What's the relation between `X1`, `elem0`, `elem1`, `elem2`...?
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24 *       Go on, now you can do it.
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