The following term cannot be read back. Please note that this is
independent of actual ISO Prolog conformance.
| ?- V = v(-(1),-((a,b)),-(-),(-)-(-)), writeq(V).
v(-1,-(a ',' b),--,- - -)
Ideally, this term is written as (please note the spaces):
v(- (1),- (a,b),- (-),(-)-(-))
Please refer to http://www.complang.tuwien.ac.at/ulrich/iso-prolog/conformity_assessment#table
for further differences.