求PASCAL语言树的三种遍历的程序

已知先序中序：
procedure Solve(pre,mid:string);
var i:integer;
begin
if (pre='') or (mid='') then exit;
i:=pos(pre[1],mid);
solve(copy(pre,2,i),copy(mid,1,i-1));
solve(copy(pre,i+1,length(pre)-i),copy(mid,i+1,length(mid)-i));
post:=post+pre[1]; {加上根，递归结束后post即为后序遍历}
end;
已知中序后序：
procedure Solve(mid,post:string);
var i:integer;
begin
if (mid='') or (post='') then exit;
i:=pos(post[length(post)],mid);
pre:=pre+post[length(post)]; {加上根，递归结束后pre即为前序遍历}
solve(copy(mid,1,I-1),copy(post,1,I-1));
solve(copy(mid,I+1,length(mid)-I),copy(post,I,length(post)-i));
end;
已知先序后序：
function ok(s1,s2:string):boolean;
var i,l:integer; p:boolean;
begin
ok:=true;
l:=length(s1);
for i:=1 to l do begin
p:=false;
for j:=1 to l do
if s1[i]=s2[j] then p:=true;
if not