type_subst : hol_type subst -> hol_type -> hol_type
type_subst theta tywill appropriately instantiate the type ty. The instantiations will be performed in parallel. If several of the type instantiations are applicable, the choice is undefined. Each redex_i ought to be a type variable, but if it isn't, it will never be replaced. Also, it is not necessary that any or all of the types redex_1...redex_n should in fact appear in ty.
- type_subst [alpha |-> bool] (Type `:'a # 'b`); > val it = `:bool # 'b` : hol_type - type_subst [Type`:'a # 'b` |-> Type `:num`, alpha |-> bool] (Type`:'a # 'b`); > val it = `:bool # 'b` : hol_type