#Java 8, <s>131</s> <s>129</s> 131 bytes

<!-- language-all: lang-java -->

    a->{java.util.Set r=new java.util.HashSet();for(String s:a)if("a->{jv.utilSe r=nwHsh();fog:\"\\cd}".contains(s))r.add(s);return r;}

+2 bytes again due to a bug-fix

**Explanation:**

[Try it here.](https://tio.run/##lZNLb9NAEMfv/RRDeNnQmGd5NG0A8eqFVigHDk2JJvbE3nS9jnbXCaFEKvSA1AOnHJAoUpHKrSeQkKrAJeUAfAqSCvExwiRtpSLEIZK99npm/vOb9UwV65hNaqSqwfLAl2gMPEChViYAhLKkK@gTzA@3AFX29VIrpFcgO3M7Qo0@u@TBdwpWCxUuLgG6OfZtTfBiLFrhwzwomIUBZvMrfwmAnlXUOCI6hybi746bqyT6QBHMNLqi4mRG4fWRY4GGoY05E41cw@liplj0g1bG8xNlGd44xnW1h0HALzlNNtUKdK41GKLxVUvLksEO@OqJCCDmsKNF7BdcaBpLsZek1quxyUrlKM93MrdkmbSFu5zKklAZz9SksE4m47qj8v8fWSyWSg4slEoLbuncGHHHbh4/cfLxqTOOWzq70nrGJc/kb4wRf@HipctTV65eu34@O7u4VCzmTk964@R39tZe/fyw@fvNOq8ub359eddvd/rt57yOodNf3ehu5U9OJr3O@retH5u8333d67z/uj51p/uxt7PW29n8/vlht1PN7b7MsTXX6n7qr74dJ0V7u99eHV3bwKQO7L3YyPLN7@4YOvdQA3/kMQAbEaTK54a3FEAZ/eUGcuMbSCoHtgr3rkgUliUBqeDQ8IhYm5uvUBMaJaCODy33UeKTJkhBBhBMjFKyjKYQdcA5miRl0gCTKg8WdFnY4SzYSLCzZf9AcPMqnkxW00kaRrIJSiiyzSyJMLIQCymZZ/jkBMMwBallFnbkrhWhEhXho7JMYC1Dl2VK2VATKahJZCVoRIkhwBplAzI@F8VYUlQIeDpjFtQEJgGM8SmzsSwfXsycdWJOhuQimzxizDHkVsvMHArLh8BH50e0L4AcRdYyPHGICAi9f/5Qa6I1@AM)

    a->{                    // Method with String-array parameter and Set return-type
      java.util.Set r=new java.util.HashSet();
                            //  The result Set
      for(String s:a)       //  Loop over the input String-array
        if("a->{jv.utilSe r=nwHsh();fog:\"\\cd}".contains(s))
                            //   If the current character is part of the source-code:
          r.add(s);         //    Add it to the Set
                            //  End of loop (implicit / single-line body)
      return r;             //  Return the result-Set
    }                       // End of method