choroba , Another tricky issue with the program is, that suppose consider this :-

child    parent    likelihood
M7    Q    P
M7    M28    E
M28    M6    E
M6    Q    Pl
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So in this case the output is coming to be M7:M7<-M28<-M6<-Q = E.E.Pl, whereas the correct output should be M7:M7<-Q which is the shortest path from M7 to Q.