Mapping isomorphism for posets or graphs

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According to the documentation of is_isomorphic, you can use the argument certificate=True:

sage: G = Graph([(0,1),(1,2)])     
sage: H = Graph([(8,9), (9,10)])                                                 
sage: G.is_isomorphic(H)                                                        
True
sage: G.is_isomorphic(H, certificate=True)                                      
(True, {0: 10, 1: 9, 2: 8})

If the automorphism group of G is non trivial, there are more than one such map. You can deduce all of them from the automorphism group of G:

sage: G.automorphism_group()                                                    
Permutation Group with generators [(0,2)]