Question: Error, (in findproot) improper op or subscript selector

Please help, here is my code:

 

findproot:=proc(f,var,k)
local i,g,B,n,L,tk;

readlib(rootbound):readlib(realroot):
B:=rootbound(f,var);
g:=expand(subs(var=B*var,f));
if B<1 then g:=numer(g);fi;
n:=degree(g,var);
L:=zero_one(g,var,n,1/B/2^k);
tk:=k+1:
while has(L,0) do
L:=zero_one(g,var,n,1/B/2^tk);
tk:=tk+1:
od:
if L=[] then RETURN([]);fi;
L:=map(proc(x,y) [op(1,x)*y,op(2,x)*y];end,L,B);
end:

 

I dont know why i cant run this code, it always report: 

Error, (in findproot) improper op or subscript selector

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