I am not sure if this really answers your question, but my understanding of the text you are quoting just says that the function mandelis another function (e.g. multiplication, min, max, addition, etc.), which may appear in your genetic program.
mandel, , (in_1 in_2) . in_1 * in_2, mandel - :
int mandel(int in_1, int in_2) {
x = 0
y = 0
iteration = 0
max_iteration = 1000
while( x*x + y*y <= (2*2) && iteration < max_iteration ) {
xtemp = x*x - y*y + in_1
y = 2*x*y + in_2
x = xtemp
++iteration
}
if( iteration == max_iteration ) return 0
else return iteration
}
mandel x, - y, (x,y) .
, , , x y. , , x, - x + 2*y? , x, mandel(x,y)?