I want to compute the fundamental group of the set C defined below :
$A_{1}:=[0,1]²,A_2:=[-1,0]\times[0,1],C=\partial A_1 \cup \partial A_2$.
I have to use the Van Kampen theorem and so I know that I must exhibit two open sets that are arc-connected [and cover the space] but I do not see how.