# [plt-scheme] Y Combinator Exercise

On Nov 16, 2005, at 12:59 PM, Matthias Felleisen wrote:
>* In the monograph on reduction semantics [Felleisen & Flatt], we had
*>* some sample calculations using the Y combinator along the lines of
*>* what John points out. Use reductions to show ((Y mk-!) 2) is 2.
*>* Then show them that the fixpoint equation helps. Reprove the first
*>* one and wow it all gets easier. Then show them that you need a
*>* calculus (=) and that reductions (->) are no longer enough for
*>* this. Puzzle: can you design a cbv Y-like combinator that doesn't
*>* use 'backwards' reductions. -- Matthias
*
<humility>
Okay, now I'm confused. Isn't cbv Y _itself_ a Y-like combinator
that doesn't use 'backwards' reductions?
</humility>
John
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