apg_typeside t apg_instance G1 : s1 apg_instance G2 : s2 apg_instance G : s1 apg_morphism h : G1 -> G2 apg_morphism h' : G1 -> G2 apg_morphism k : G -> G1 ---------------------------------- apg_morphism (equalize_u h h' k) : G -> equalize h h'Equalizer universal property mediating morphism of two parallel morphisms in the category of APGs.