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    1% Graph
    2
    3node(a).
    4node(b).
    5node(c).
    6node(d).
    7node(e).
    8
    9edge(a,b).
   10edge(a,c).
   11edge(b,c).
   12edge(d,e).
   13
   14path(X,X).
   15path(X,Y):-edge(X,Z),path(Z,Y)