 Graphs that have vertices representing events , and edges representing causal relations between events , are often acyclic – arranging the vertices in linear order of time , all arrows point in the same direction as time , from parent to child ( due to causality affecting the future , not the past ) , and thus have no loops . 
 Graphs <a href='null_relcl' title='1'><mark>that</mark></a><a href='got' title='2'><mark>have</mark></a> vertices representing events , and edges representing causal relations between events , <a href='drop_aux' title='3'><mark>are</mark></a>often acyclic – arranging the vertices in linear order of time , all arrows point in the same direction as time , from parent to child ( due to causality affecting the future , not the past ) , and thus <a href='got' title='4'><mark>have</mark></a> no loops . 
Graphs got vertices representing events , and edges reppin causal relations between events , often acyclic – arranging da vertices in linear order of time , all arrows point in tdasame direction as time , from parent to child ( due to causality affecting the future , not the past ) , and thus got no loops .