This alter table command references the column *tsn_accepted* in the
*taxonomic_units* table yet there is no such column in that table.
There however is a *tsn* in column taxonomic_units. A column named*
tsn_accepted* is found in the *synonym_links* table. Should the
instructions read (see below) or am I just reading the instructions
alter table "itis".synonym_links add constraint (foreign key
you added foreign key (synonym_links.tsn_accepted) which is referencing to primary key in table taxonomic_units.
"contraint "itis".supercede means that you declared the name of the new contraint. This name must be unique among the names of indexes and constraints in database.
But this part is not obligatory when you dont declare the name then IDS automatically does.