I have a dynamic equation of consumption :

and the code in a book is:

# #mar_c= (c^theta*(1-lab)^(1-theta))^(1-tau);

# #mar_c1=(c(+1)^theta*(1-lab(+1))^(1-theta))^(1-tau);

mar_c/c=beta*(mar_c1/c(+1))*(1+alpha*exp(z)*k(-1)^(alpha-1)*lab^(1-

alpha)-delta);

why the variable of K shifts 2 periods and variable lab shifts 1 period? in the equation above, the period of K and lab are both (t+1),