<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _compare_across(collections, key):
 """Return whether all the collections return equal values when called with `key`."""

    if len(collections) < 2:
        return True
    c0 = key(collections[0])
    return all(c0 == key(c) for c in collections[1:])