I believe the process by which we compute a performing a wildcard capture
conversion should include the formal type parameter's bounds in the result,
using glb(). The following example shows why. In this case we have an example
of G1<? extends I2> being a subtype of G1<?>, yet an operation that succeeds on
the latter will fail on the former.

==========$ cat -n T.java
     1 interface I1 {
     2 void i1();
     3 }
     4
     5 class G1<T extends I1> {
     6 T get() { return null; }
     7 }
     8
     9 interface I2 {
    10 void i2();
    11 }
    12
    13 class Main {
    14 void f1(G1<?> g1) {
    15 g1.get().i1();
    16 }
    17 void f2(G1<? extends I2> g1) {
    18 g1.get().i1(); // oops!
    19 g1.get().i2();
    20 }
    21 }
==========$ javac T.java
T.java:18: cannot find symbol
symbol : method i1()
location: interface I2
        g1.get().i1(); // oops!
              ^
1 error
==========$