Question: Error, reserved word `then` unexpected

Hi, I have created a procedure and it keeps giving the error "Error, reserved word `then` unexpected". What am I doing wrong?

local L,a,b;
L:=(`[]`@ op)~(indets(P, indexed));
a:=Search(1,L[1]); b:=Search(2,L[1]);
 if a<>0 and b<>0 then print("mixed");
 elif a<>0 and b=0 then print("t-only");
 elif a=0 and b<> then print("x-only") ; end if;
 end proc:

Product: Maple 2021

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