Improved error message, suggesting addition of type constraints if occurrences of the recursive set remain in the fixedpoint definition.

Now def of apfst uses pattern-matching

improved indentation

New function read_cterms is a combination of read_def_cterm and read_cterm. It reads and simultaneously type-checks a list of strings. cterm_of no longer catches exception TYPE; instead it must be caught later on and a message printed using Sign.exn_type_msg. More informative messages can be printed this way.

exports exn_type_msg for error messages. Calls new infer_types. Improved comments.

infer_types now takes a term list and a type list as argument. It is defined using the new function infer_terms. Error messages and comments also improved.