Consider the following code:
In[1]:= l1={3,3,3}
Out[1]= {3,3,3}
In[2]:= l2={1,2,3}
Out[2]= {1,2,3}
In[4]:= ForAll[x,MemberQ[l1,x],Exists[y,MemberQ[l2,y],x==y]]
Out[4]= True
In[3]:= Exists[z,MemberQ[l2,z],ForAll[u,MemberQ[l1,u],z==u]]
Out[3]= False
In[5]:= Exists[z,MemberQ[l2,z_],ForAll[u,MemberQ[l1,u],z==u]]
Out[5]= True
"WHY z HAVE TO BE SET TO PATTERN z_ TO GET RIGHT RESULT?"
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