function onCommand( id ) {
		var cache;
		var keys;
		var FLG;
		var err;
		var key;
		var ws;
		var i;
		var o;

		cache = repl._internal.presentation.cache;
		if ( arguments.length ) {
			if ( !isString( id ) && !isNonNegativeInteger( id ) ) {
				err = new TypeError( format( 'invalid argument. Invalid presentation identifier. Must be either a string or nonnegative integer. Value: `%s`.', id ) );
				debug( 'Error: %s', err.message );
				repl._ostream.write( 'Error: '+err.message+'\n' );
				return false;
			}
			key = id;
		} else {
			ws = repl._currentWorkspace;
			keys = objectKeys( cache );
			for ( i = 0; i < keys.length; i++ ) {
				if ( cache[ keys[ i ] ].w === ws ) {
					key = cache[ keys[ i ] ].i;
					break;
				}
			}
			if ( key === void 0 ) {
				err = new Error( 'invalid invocation. Not currently in a presentation workspace. Must provide either a string or nonnegative integer which corresponds to the identifier of the presentation to be stopped.' );
				debug( 'Error: %s', err.message );
				repl._ostream.write( 'Error: '+err.message+'\n' );
				return false;
			}
		}
		if ( !hasOwnProp( cache, key ) ) {
			debug( 'Unrecognized presentation identifier: %d', key );
			return false;
		}
		debug( 'Stopping presentation: %d', key );

		// Retrieve the presentation data:
		o = cache[ key ];

		// Delete the presentation workspace...
		if ( o.w !== 'base' ) {
			debug( 'Deleting workspace: %s', o.w );
			FLG = repl._quiet;
			repl._quiet = true; // temporarily silence logging
			repl._context.deleteWorkspace( o.w );
			repl._quiet = FLG;
		}
		// Ensure that we no longer watch presentation files (if enabled):
		o.p.unwatch();

		// Update the internal resource cache for tracking presentations:
		delete cache[ key ];

		return true;
	}
Stops a REPL presentation.

@private
@param {(NonNegativeInteger|string)} [id] - presentation identifier
@returns {boolean} boolean indicating whether a REPL presentation is successfully stopped