1. According to doc:
If at least one init function is given,
...
The longest parameter list (which is necessarily unique) is called the "common suffix".


Actually 'init' with same parameter lists are permitted, see attached example Loop0.java.

2. Setp2.d declares 'effectively identical to...' although
'The term "effectively identical", applied to parameter type lists, means that they must be identical, or else one list must be a proper prefix of the other.'

The definition looks like symmetrical relation (because there is no difference in 'one' and 'another'). Step2.d uses 'effectively identical' in different (directional) way.

See attached example Loop1.java:
E.g.
init ()I
step (I)I

Common parameter sequence: 'I'
pred (I, I, I)Z and fini (I, I, I)I
both have effectively identical with 'I' lists.