Dear Biswajit, it doesn't hurt opening a question with a friendly sentence.
Anyway, as the output tells you, your graph vertices are labelled by strings (namely "x0", "x1", ...) which you cannot multiply as the product of two strings is not defined here. If you want to use variables instead, you do for example sage: P.<x0,x1,x2,y1,y2> = PolynomialRing(QQ,5) sage: dia = DiGraph({x0:{x1:(1, -1),y1:(1, -1),x2:(1, -1)},y2:{x0:(1, -1),x1:(1, -1)}}) sage: diaout = dia.neighbors_out(x0);diaout [y1, x2, x1] sage: prod(diaout) x1*x2*y1 Cheers, Christian -- You received this message because you are subscribed to the Google Groups "sage-combinat-devel" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-combinat-devel+unsubscr...@googlegroups.com. To post to this group, send email to sage-combinat-devel@googlegroups.com. Visit this group at https://groups.google.com/group/sage-combinat-devel. For more options, visit https://groups.google.com/d/optout.