What does "Program type already present" mean? : <p>I'm trying to build an app in Android Studio.  After adding the Eclipse Paho library as a gradle dependency(or is it Maven?  I'm new to the Android ecosystem), I got the following error:</p>

<pre><code>Program type already present: android.support.v4.accessibilityservice.AccessibilityServiceInfoCompat
Message{kind=ERROR, text=Program type already present: android.support.v4.accessibilityservice.AccessibilityServiceInfoCompat, sources=[Unknown source file], tool name=Optional.of(D8)}
</code></pre>

<p>I've checked many different StackOverflow questions relating to this error, but the answers are all specific to certain libraries.  <strong>I'm looking not only for a solution to the error, but an understanding of what the error <em>means</em>.</strong>  That way it'll be easier for people to figure out solutions for their specific cases.  So far, no answer has provided that.</p>

<p>From other StackOverflow answers, I've gathered that it has something to do with my gradle file.  So, here's app/build.gradle:</p>

<pre><code>apply plugin: 'com.android.application'
android {
    compileSdkVersion 27
    defaultConfig {
        applicationId "---REDACTED FOR PRIVACY---"
        minSdkVersion 15
        targetSdkVersion 27
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}
dependencies {
    implementation fileTree(include: ['*.jar'], dir: 'libs')
    implementation 'com.android.support:appcompat-v7:27.1.0'
    implementation 'com.android.support:support-media-compat:27.1.0'
    implementation 'com.android.support:support-v13:27.1.0'
    implementation 'com.google.android.gms:play-services-maps:12.0.1'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'com.android.support.test:runner:1.0.1'
    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.1'
    implementation 'com.android.support.constraint:constraint-layout:1.0.2'
    implementation 'org.eclipse.paho:org.eclipse.paho.client.mqttv3:1.0.2'
    implementation 'org.eclipse.paho:org.eclipse.paho.android.service:1.0.2'
}

repositories {
    maven { url 'https://repo.eclipse.org/content/repositories/paho-releases/' }
} 
</code></pre>
