twitter bootstrap get an error on less compile

Question

i'm would like to use twitter bootstrap but assigning bootstrap classes at my own class i get a compile error

for example

.myRow { .row-fluid; }
.myRowSpan { .row-fluid .span4; }

i'm using codekit compiler for less, and i import bootstrap at the top

@import "./bootstrap.less";
@import "./responsive.less";

now on myRow it is ok, but on myRowSpan i get an error

NameError: .row-fluid.span4 is undefined in my.css

Answer 1

use:

@import "./bootstrap.less";
@import "./responsive.less";
.myRow { .row-fluid; }
.myRowSpan { #grid .fluid .span(4); }