buy inserting in formula

["Tom Supera" <tom_supera@xxxx>]

Hi,
How can i use the buy value (close, rsi,..) in 
my formula.
Example: I want a sell signal, if the close 
is smaller than the close on the buy day.
 
Sell = C < R<FONT 
color=#0000ff>ef (C,Buy) or <FONT 
color=#0000ff>BarsSince (Buy) == <FONT 
color=#ff00ff>3;

Can anyone help me.
Tom Supera