allowed_type_constant : string -> bool
STRUCTURE
Lexis
SYNOPSIS
Tests if a string has a permissible name for a type constant.

LIBRARY
Lexis
DESCRIPTION
When applied to a string, allowed_type_constant returns true if the string is a permissible constant name for a type operator, and false otherwise.
FAILURE
Never fails.
EXAMPLE
The following gives a sample of some allowed and disallowed names for type operators: 
   - map Lexis.allowed_type_constant ["list", "'a", "fun", "->", "#", "fun2"];
   > val it = [true, false, true, false, false, true] : bool list

COMMENTS
Note that this function only performs a lexical test; it does not check whether there is already a type operator of that name in the current theory.

This function is not currently enforced by the system, as it was found that more flexibilty in naming was preferable.

SEEALSO
allowed_term_constant
HOL  Kananaskis-14