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Behaviour of Replace

• To: mathgroup at smc.vnet.net
• Subject: [mg114852] Behaviour of Replace
• From: Peter Breitfeld <phbrf at t-online.de>
• Date: Mon, 20 Dec 2010 00:40:28 -0500 (EST)

Suppose I have this nested list:

demo = {1, {2, {3, {4, {5, {6, {7, {8, 8}}}}}}}}

Replace[demo, {x_, y_} :> {x, a, y}, -1]

Out={1, {2, a, {3, a, {4, a, {5, a, {6, a, {7, a, {8, a, 8}}}}}}}}

I expected to have an a after the 1 too, what I tried to get using

Replace[demo,{x_,y_}:>{x,a,y},-1,Heads->True]

but this gives the same result as above. But this will do what I wanted:

Replace[demo, {x_, y_} :> {x, a, y}, {0, 8}]

Out={1, a, {2, a, {3, a, {4, a, {5, a, {6, a, {7, a, {8, a, 8}}}}}}}}

Can somone please explain this behaviour? What I found was that

Level[demo,{0}] returns {{1},{2,{3...} beeing {demo}

Thank you
-- 
_________________________________________________________________
Peter Breitfeld, Bad Saulgau, Germany -- http://www.pBreitfeld.de

• Follow-Ups:
  • Re: Behaviour of Replace
    • From: Andrzej Kozlowski <akoz@mimuw.edu.pl>