Actually the 2nd edition of Curly Girl (Lorraine Massey's book) does recognize sulfate-free shampoos (low-poos) as an alternative to conditioner washing (in explaining cleansing she states to use a botanical conditioner or sulfate free shampoo). I know of several people who cannot co-wash and exclusively use low-poos and will absolutely correct you if you tell them that they are not CG.

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3a/f/iii
Modified CG since 11/5/11
CLEANSE: VO5 Vanilla Mint Tea Clarifying, DevaCare No-Poo, CHS Treatment Shampoo
RO: DevaCare One Condition, SS Caitlin's Conditioner, Mop Top Daily Conditioner
LI: SS Repairing Protein Treatment, CHS Silk Leave-In
STYLE: Re:Coil, Curl Keeper, Deva Ultra Defining Gel, Curls Rock Amplifier and Strong Hold Mousse, Sweet Curls Elixirs Okra Gel and Hard Hold Gel, SS Curl Enhancing Jelly and Firm Hold Gel