I am writing this function in sml fun removeNodeswithNoIncoming((x:int,y)::xs,element:int) = if x=element then removeNodeswithNoIncoming (xs , element) else (x,y) :: removeNodeswithNoIncoming (xs , element) | removeNodeswithNoIncoming(nil,element) = nil; the function takes list of tuples [(0,0),(0,1)(1,2)] and another element 0 if first element of the tuples is same as second parameter , it removes it from the list The o/p for the above list should be [(1,2)] Unfortunately , the code is not working for the above input. Though there are other inputs for which it works - removeNodeswithNoIncomingEdge([(0,1),(0,2),(1,2)],0); stdIn:30.1-30.30 Error: unbound variable or constructor: removeNodeswithNoIncomi ngEdge - removeNodeswithNoIncomingEdge([(0,1),(0,2),(1,2),(1,4)],0); stdIn:1.2-1.31 Error: unbound variable or constructor: removeNodeswithNoIncoming Edge