In[]:=
euclidData=ResourceData["Theorem Network from Euclid's Elements"];
In[]:=
baseTheorem=VertexOutComponent[ReverseGraph[euclidData],<|"Book"->1,"Theorem"->6|>]
Out[]=
{Book1,Theorem6,Book2,Theorem4,Book2,Theorem9,Book2,Theorem10,Book3,Theorem25,Book4,Theorem9,Book4,Theorem10,Book4,Theorem14,Book6,Theorem3,Book13,Theorem7,Book13,Theorem8,Book2,Theorem12,Book9,Theorem15,Book10,Theorem26,Book10,Theorem36,Book10,Theorem37,Book10,Theorem38,Book10,Theorem41,Book10,Theorem42,Book10,Theorem44,Book10,Theorem47,Book10,Theorem54,Book13,Theorem2,Book10,Theorem60,Book4,Theorem11,Book13,Theorem18,Book13,Theorem17,Book13,Theorem11,Book10,Theorem43,Book10,Theorem45,Book10,Theorem46,Book10,Theorem79,Book10,Theorem80,Book10,Theorem82,Book10,Theorem83,Book10,Theorem48,Book10,Theorem49,Book10,Theorem50,Book10,Theorem52,Book10,Theorem53,Book10,Theorem61,Book10,Theorem62,Book10,Theorem63,Book10,Theorem64,Book10,Theorem65,Book10,Theorem66,Book10,Theorem71,Book10,Theorem72,Book10,Theorem112,Book10,Theorem113,Book10,Theorem55,Book10,Theorem67,Book10,Theorem56,Book10,Theorem59,Book10,Theorem70,Book10,Theorem91,Book10,Theorem111,Book4,Theorem12,Book4,Theorem16,Book13,Theorem16,Book10,Theorem81,Book10,Theorem84,Book10,Theorem114,Book10,Theorem108}
In[]:=
Length[baseTheorem]
Out[]=
64