Example for remove with predicate is the following:

int[] a = [ 1, 2, 3, 2, 3, 4, 5, 2, 5, 6 ];
assert(a[0 .. remove!("a == 2")(a).length] == [ 1, 3, 3, 4, 5, 5, 6 ]);

This example is confusing because the array is named 'a' and the predicate placeholder is also named 'a'.  Yes, reading the predicate blurb at the top says that 'a' is a predicate var, but if the example used 2 different names, it would at least alert the impatient reader about this assumption more clearly.  I suggest:

int[] r = [ 1, 2, 3, 2, 3, 4, 5, 2, 5, 6 ];
assert(r[0 .. remove!("a == 2")(r).length] == [ 1, 3, 3, 4, 5, 5, 6 ]);