inst : (hol_type,hol_type)subst -> term -> term
Performs type instantiations in a term.
The function inst should be used as follows:
   inst [{redex_1, residue_1},...,{redex_n, residue_n}] tm
where each ‘redex’ is a hol_type variable, and each ‘residue’ is a hol_type and tm a term to be type-instantiated. This call will replace each occurrence of a redex in tm by its associated residue. Replacement is done in parallel, i.e., once a redex has been replaced by its residue, at some place in the term, that residue at that place will not itself be replaced in the current call. Bound term variables may be renamed in order to preserve the term structure.
Never fails. A redex that is not a variable is simply ignored.
- show_types := true;
> val it = () : unit

- inst [alpha |-> Type`:num`] (Term`(x:'a) = (x:'a)`)
> val it = `(x :num) = x` : term

- inst [bool |-> Type`:num`] (Term`x:bool`);
> val it = `(x :bool)` : term

- inst [alpha |-> bool] (mk_abs(Term`x:bool`,Term`x:'a`))
> val it = `\(x' :bool). (x :bool)` : term

HOL  Kananaskis-14