Problem $1.$ Consider the following type declarations

TYPE

A$1$ : float;

A$2$ : pointer to float;

A$3$ : pointer to integer;

T$1$ : structure $\{$ x : float; $\}$

T$2$ : structure $\{$ x : A$1$; $\}$

T$3$ : structure $\{$ a : float; b : integer; $\}$

T$4$ : structure $\{$ b : integer; a : float; $\}$

T$5$ : structure $\{$ a : pointer to T$5$; b : pointer to T$6$; c : pointer to T$7$; $\}$

T$6$ : structure $\{$ a : pointer to T$6$; b : pointer to T$5$; c : pointer to T$5$; $\}$

T$7$ : structure $\{$ a : pointer to T$6$; b : pointer to T$7$; c : pointer to T$9$; $\}$

T$8$ : structure $\{$ a : pointer to T$7$; b : pointer to T$6$; c : pointer to T$10$; $\}$

T$9$ : array $[4][5]$ of T$5$; $//$ array $4$ rows $5$ columns

T$10$ : array $[4][5]$ of T$2$;

Assuming the most permissive definition of structural equivalence, which types are structurally equivalent?