conditionnal rule

*To*: mathgroup at smc.vnet.net*Subject*: [mg51499] conditionnal rule*From*: darkness_wizard at hotmail.com (Wishmaster7)*Date*: Wed, 20 Oct 2004 01:21:19 -0400 (EDT)*Sender*: owner-wri-mathgroup at wolfram.com

hi all !! I want to apply a rule under a certain condition. here is the example : myList = {{a, b}, {c, d}}; myList //. {a,x_}->{a,d} apply this rule if Length[x]===1 (this means that x can not be a list) I tried something like : myList //. {a_,x_}->{c,d}/;Length[x]===1 or myList //. {a_,x_?Length[x]===1}->{c,d}/ but it does not work. can someone help me ?

**Follow-Ups**:**Re: conditionnal rule***From:*Tomas Garza <tgarza01@prodigy.net.mx>

**Re: conditionnal rule***From:*Andrzej Kozlowski <akoz@mimuw.edu.pl>