Question: cluster analysis sing maple syntax... problem

Strings := {"buffalo", "zebra", "aardvark", "aardwolf", "anteater", "antelope", "bumblebee"};
{"buffalo", "zebra", "aardvark", "aardwolf", "anteater",

"antelope", "bumblebee"}
CP := {seq(seq(StringTools:-Take(x, StringTools:-CommonPrefix(x, y)), x in Strings), y in Strings)};
P := table(map(proc (x) options operator, arrow; x = "" end proc, Strings));
for x in CP do for y in `minus`(CP, {x}) do if `and`(StringTools*IsPrefix(y, x), `implies`(assigned(P[x]), StringTools*IsPrefix(P[x], y))) then P[x] := y end if end do end do;
Error, cannot determine if this expression is true or false: StringTools*IsPrefix("a", "")

Hi I tried to apply these command in maple to see hoe cluster graphic after that can work .. but i face this problem ,

I am a begginer in maple working on it for a term paper to demonstrate it is ability to view the cluster analysis .

if u have any benefcial resources I ll be so happy.

thanks very much